A SYNTHESIS ON STUDDED TIRES - wsdot.wa.gov · Research Report Research Project Agreement T9903,...

Research Report Research Project Agreement T9903, Task 92

Studded Tires

A SYNTHESIS ON STUDDED TIRES

by

Michael J. Angerinos Joe P. Mahoney Lt. Commander Professor of Civil Engineering United States Navy University of Washington

Robyn L. Moore Amy J. O’Brien Pavement and Soils Engineer (Retired) Technical Communications Specialist Washington State Dept. of Transportation Washington State Transportation Center

Washington State Transportation Center (TRAC) University of Washington, Box 354802

University District Building 1107 NE 45th Street, Suite 535

Seattle, Washington 98105-4631

Washington State Department of Transportation Technical Monitor

Linda Pierce Pavement and Soils Engineer, Materials Laboratory

Prepared for

Washington State Transportation Commission Department of Transportation

and in cooperation with U.S. Department of Transportation

Federal Highway Administration

August 1999

TECHNICAL REPORT STANDARD TITLE PAGE1. REPORT NO. 2. GOVERNMENT ACCESSION NO. 3. RECIPIENT'S CATALOG NO.

WA-RD 471.1

4. TITLE AND SUBTITLE 5. REPORT DATE

A Synthesis on Studded Tires August 19996. PERFORMING ORGANIZATION CODE

7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO.

Michael J. Angerinos, Joe P. Mahoney, Robyn L. Moore,Amy J. O’Brien9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO.

Washington State Transportation Center (TRAC)University of Washington, Box 354802 11. CONTRACT OR GRANT NO.

University District Building; 1107 NE 45th Street, Suite 535 Agreement T9903, Task 92Seattle, Washington 98105-463112. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED

Washington State Department of TransportationTransportation Building, MS 7370

Research report

Olympia, Washington 98504-7370 14. SPONSORING AGENCY CODE

15. SUPPLEMENTARY NOTES

This study was conducted in cooperation with the U.S. Department of Transportation, Federal HighwayAdministration.16. ABSTRACT

In the winter of 1998, the Washington State Department of Transportation (WSDOT) proposedlegislation to amend the Revised Code of Washington with respect to studded tires. In April 1999,legislation was passed that changed Washington’s laws regarding studded tire use. These legislativechanges were intended to reduce pavement wear on Washington state’s highway system caused bystudded tires without losing any of the safety benefits that tire studs provide.

From the time that studded tires were first introduced, the advantages, disadvantages, and effects ofstudded tires on vehicles, drivers, and pavement systems have been the object of research and controversy.Some states have chosen to ban the use of studded tires altogether, while others, such as Oregon and nowWashington, have passed legislation that is intended to reduce the road wear impacts of studs.

This report presents a brief history of the studded tire. The report also explores the relationshipbetween pavement wear and developments in studded tires that have taken place over the past 40 years.This information should provide a background that helps to support and explain the amendments to theRevised Code of Washington regarding studded tires.

17. KEY WORDS 18. DISTRIBUTION STATEMENT

Studs, tires, studded tires, pavement wear rates,studded tire legislation

No restrictions. This document is available to thepublic through the National Technical InformationService, Springfield, VA 22616

19. SECURITY CLASSIF. (of this report) 20. SECURITY CLASSIF. (of this page) 21. NO. OF PAGES 22. PRICE

None None

DISCLAIMER

The contents of this report reflect the views of the authors, who are responsible

for the facts and the accuracy of the data presented herein. The contents do not

necessarily reflect the official views or policies of the Washington State Transportation

Commission, Department of Transportation, or the Federal Highway Administration.

This report does not constitute a standard, specification, or regulation.

ACKNOWLEDGMENTS

These individuals offered their time and advice during critical study periods:

• Dave Bowers, WSDOT Roadway Maintenance Engineer, Field OperationsSupport Service Center, Olympia, Washington

• John Lees, Northwest Regional Tire Sales Manager, Costco, Issaquah,Washington

• Chuck McGee, CEO, McGee and Co., Denver, Colorado

• Dick Nordness, Executive Director, Northwest Tire Dealers Association,Kennewick, Washington

• Don Petersen, Federal Highway Administration, Olympia, Washington

v

CONTENTS

Section Page

Executive Summary.......................................................................................................ix

1. Introduction.................................................................................................................1Study Approach.....................................................................................................1Report Organization..............................................................................................2

2. The Studded Tire: Past to Present.............................................................................3Tire Stud Characteristics.......................................................................................3

Development and Stud Types .........................................................................3Stud/Tire Interaction .......................................................................................7Evolution: Changes in Stud Length and Weight.............................................7

Marketing the Studded Tire ................................................................................12Studded Tire Usage Rates...................................................................................15Laws and Restrictions for Studded Tire Use ......................................................16

3. Pavement Wear .........................................................................................................23Mechanisms of Pavement Wear..........................................................................23Pavement Wear Studies ......................................................................................23

Early Indications ...........................................................................................23Minnesota Comparisons, 1972......................................................................25Applicability and Comparability of Past Research.......................................28Alaska Study, 1990 .......................................................................................30Continuing Research in Scandinavia ............................................................31Wear Trends..................................................................................................32

Factors that Affect Pavement Wear ....................................................................33Vehicle ..........................................................................................................35Tires ..............................................................................................................36Studs..............................................................................................................36Pavement.......................................................................................................39Temperature ..................................................................................................39

4. Studded Tires in Washington State.........................................................................41Studded Tire Impacts on the WSDOT Route System.........................................41Oregon Legislation..............................................................................................42Proposed Washington State Law Revision .........................................................441999 Washington State Law Revision................................................................45Conclusions and Recommendations ...................................................................46

References......................................................................................................................48

Bibliography ..................................................................................................................50

Appendix A. Miscellaneous Facts and Figures from the 1997 Winter TrafficConference, Ivalo, Finland

Appendix B. New Technology Winter Tires

vi

FIGURES

Number Page

1 First generation single-flange tire stud...................................................................4

2 First tire studs with tungsten carbide cores............................................................4

3 Cross-sectional view of single-flanged tire stud....................................................5

4 Tire stud before and after break-in-period. ............................................................8

5 Comparison between the CP tire stud and the conventional stud........................10

6 States which allowed studded tires as of January 1, 1967. ..................................15

7 Legal restrictions on use of studded tires in 1975................................................18

8 The effect of temperature and water on the wearing of pavements. ....................40

vii

TABLES

Number Page

1 Stud type and basic characteristics as of 1972.......................................................6

2 Change of average tire stud pin protrusion by year. ..............................................8

3 Increase in use of studded tires during initial U.S. marketing period(1963–1966).........................................................................................................14

4 Historical data on estimated percentage of studded tire use in 1972...................17

5 1990 restrictions on use of studded tires..............................................................19

6 1995 restrictions on use of studded tires..............................................................21

7 Mechanisms of pavement wear under studded tires. ...........................................23

8 Summary of tests (1966 and 1967) on wear of pavement surface by studdedtires.......................................................................................................................26

9 Depth of pavement surface wear in Minnesota at typical test points.................. 27

10 Historical summary of road wear studies.............................................................29

11 Juneau pavement wear per million studded tire passes........................................31

12 Factors affecting pavement wear. ........................................................................34

13 Pavement wear due to vehicle speed....................................................................35

14 Allowable number of studs by tire size................................................................37

15 Pavement wear due to stud weight.......................................................................38

ix

EXECUTIVE SUMMARY

In the winter of 1998, the Washington State Department of Transportation

(WSDOT) proposed legislation to amend the Revised Code of Washington with respect to

studded tires. In April 1999, legislation was passed that changed Washington’s laws

regarding studded tire use. These legislative changes were intended to reduce pavement wear

on Washington state’s highway system caused by studded tires without losing any of the

safety benefits that tire studs provide.

From the time that studded tires were first introduced, the advantages, disadvantages,

and effects of studded tires on vehicles, drivers, and pavement systems have been the object

of research and controversy. Some states have chosen to ban the use of studded tires

altogether, while others, such as Oregon and now Washington, have passed legislation that

is intended to reduce the road wear impacts of studs.

One objective of this report is to present a brief history of the studded tire. The

report also explores the relationship between pavement wear and developments in studded

tires that have taken place over the past 40 years. This information will provide a

background that helps to support and explain the amendments to the Revised Code of

Washington regarding studded tires.

STUDY APPROACH

These objectives were accomplished through an extensive review of world-wide

literature covering research on studded tires—their evolution and their relationship to

pavement wear—most of which was conducted from 1966 through 1975. The study also

looked at new developments in studded tire features and their impacts on pavement wear.

The primary source of information on these recent developments is research within

Scandinavia.

This report deals in a limited manner with studded tire performance.

x

DEVELOPMENT OF TIRE STUDS

According to Cantz (1972), metallic cleats were used in pneumatic tires over 100

years ago (1890). These cleats were used to increase the wear resistance of tires against the

difficult gravel road conditions that generally existed at that time.

Tire studs consist of two primary parts. The outside part of the stud is called a

jacket or body, which is held in the tire tread rubber by a flange at the base. The core/insert

or pin is the element that protrudes beyond the tire surface and contacts the pavement

surface. The first true studs, which incorporated tungsten carbide cores (still used today)

were used in Scandinavia in the late 1950s. The use of tungsten carbide enabled the wear of

the stud to be similar to the wear of the tire tread.

The design of tire studs has evolved dramatically since they were first introduced in

the early 1960s. In particular, two major elements that contribute to pavement wear, stud

protrusion length and stud weight, have been significantly improved. These changes are

described below.

EFFECTS OF STUDS ON PAVEMENT WEAR

Data from Brunette (1995), the Washington State Pavement Management System

(1996), and Malik (1994), show that the pavement wheelpath wear reported by different

states varies widely (see below). In general, the wear per one million studded tire passes is

significantly higher for asphalt concrete pavement surfaces in comparison to PCC surfaces

when both values are reported for an individual state. The lowest wear rates are for

Washington State and Alaska, which is not unexpected because of the higher quality

aggregate generally available in these two states.

A number of stud-related factors have been found to affect pavement wear. Five of

the most important are the following:

• stud protrusion

• stud weight

xi

• driving speed

• number of studs per tire

• stopping effectiveness.

These are discussed below.

Stud Protrusion

Stud protrusion has been directly linked to pavement wear and, naturally, the more

the protrusion the more the wear. Over the last 30 years or so, softer tungsten carbide has

been adopted which has helped reduce tire-stud protrusion. Cantz (1972) noted that stud

protrusion was generally 2.2 mm in 1966 and had decreased to 1.7 mm by 1971. Today,

stud protrusion is closer to 1.2 to 1.5 mm. By 1971 stud wear had been reduced by about

25 percent over 1966 conditions, and today that reduction is almost 40 percent.

Stud Weight

Stud weight has been directly related to pavement wear in numerous studies

conducted both in the United States and Europe. Work performed at The Technical

Research Center of Finland (VTT) and recently summarized by Unhola (1997) shows how

0 0.1 0.2 0.3 0.4 0.5 0.6

Washington State PCC (Seattle and Spokane)

Washington State AC Class D

Oregon AC

Oregon PCC

Minnesota PCC

California AC Low Estimate

Alaska AC High Estimate

Alaska AC Low Estimate

Wheelpath Wear(inches per million studded tire passes)

xii

stud weight increases pavement wear. (The Finnish findings were later confirmed by

research done in Sweden.) The Finnish results can be summarized in terms of cubic

centimeters (cm3) of pavement wear as a function of stud weight:

1.0 grams stud mass: 0.25 cm3 wear.





Information provided by the tire industry indicates that currently, studs supplied for

most passenger cars in Western Washington typically weigh about 1.7 to 1.9 grams. A

reduction in stud weight to 1.5 grams would potentially reduce wear by about 12 to 13

percent. A reduction to 1.1 grams (the standard maximum stud weight used in most of

Scandinavia for passenger car tires) could potentially reduce wear by about 30 percent.

Number of Studs

The number of studs per tire has been limited by most of Scandinavian countries

(Unhola 1997) but not in the United States. The maximum number of studs is not likely a

major issue here. For one reason, the more studs a dealer installs, the more expensive the

tire.

Driving Speed

Driving speed can have a significant impact on pavement wear caused by studded

tires. Unhola (1997) summarized work done at VTT that examined this issue. The results

can also be characterized in terms of pavement wear (cm3):

Speed = 50 km/h (30 mph): 0.20 cm3 wear.




xiii

These results suggest that changing the Interstate rural speed limit from 55 mph (89

km/h) to 70 mph (113 km/h) has potentially doubled pavement wear caused by studded

tires. In comparison with speed limits more appropriate for city streets (30 mph (50 km/h)),

70 mph Interstate speeds mean an increase in pavement wear by a factor of four.

Stopping Distances

Stopping distance studies have been performed in the United States, Canada, and

other countries to compare studded tire performance with various types of tires. One major

study performed in Canada was reported by Smith and Clough (1972). This early 1970s

test (winter of 1970-1971) was conducted to evaluate various tires under winter driving

conditions. The results showed that all tire configurations performed about the same on

both clear ice and sanded ice at 0°F. At 32°F, the differences between clear ice and sanded

ice were significant, a reduction of 62 percent in stopping distance (or 411 ft. versus 157 ft.)

on average for all tire configurations. As expected, sedans equipped with four studded tires

performed better than studded tires on the rear wheels only, with stopping distance

reductions of 28 and 10 percent, respectively, over standard highway tires. On sanded ice,

the same configurations resulted in reductions of 17 and 34 percent, respectively. These

comparisons showed that sand applied to ice offers a marginal benefit at very cold

temperatures (i.e., 0°F), with all stopping distances ranging between 4.6 to 5.2 times greater

than wet asphalt concrete. However, at 32°F, the sand application picture changes

dramatically, with stopping distances being reduced to 1.8 to 3.0 times greater than wet

asphalt concrete.

SURVEY OF NORTH AMERICAN STUDDED TIRE USAGE

A survey conducted by Brunette (1995) asked 25 state departments of transportation

various questions related to studded tires. One question was, “Does your state permit

studded tire use?” Of the 25 states that responded, all but three allow studded tires. The

xiv

three states that do not are Illinois, Indiana, and Minnesota (Minnesota does allow the use of

studs for rural mail carriers). All of the four Canadian provinces that responded to the

question currently allow the use of studded tires.

Brunette asked about the allowable time period during which studded tires can be

used. As shown below, of the 20 states that responded to the question, over 50 percent

allow studs for 5 to 5.5 months (typically starting on October 15 or November 1 and ending

April 1 or April 15). Current Washington State law allows their use from November 1 to

April 1.

A survey conducted by WSDOT during the winter of 1996-1997 revealed that, on

average, 10 percent of passenger vehicles use studded tires in Western Washington and 32

percent in Eastern Washington (the percentages are based on two studded tires per vehicle).

The surveys were taken in parking lots and garages at 14 locations. Of these locations, the

lowest stud usage was observed in Puyallup (6 percent) and the highest in Spokane (56

percent).

2

7

4

1

2

3

1

0 5 10

• Montana

• Alaska (North of Lat 60), Maine,Nevada

• Alaska (South of Lat 60), New York

• Oregon

• Connecticut, Minnesota, NewJersey, Utah

• California, Iowa, Kansas,Maryland, Nebraska, North Dakota,

Washington

• Michigan, Rhode Island

Number of State DOTs

(Allowed 4.5 Months)

(Allowed 7.5 months)





(5.0 months)

Allowable Studded Tire Use Durations for State DOTs (after Brunette (1995))

xv

STUDDED TIRE IMPACTS ON THE WSDOT ROUTE SYSTEM

Studded tires cause accelerated pavement damage, with some pavement surfaces

being more susceptible than others. The wear rates for WSDOT Class D open-graded

wearing course has been judged unacceptable, and it is rarely used on high volume routes

today. This paving material was used to reduce noise, as well as enhance pavement friction

and reduce splash and spray during wet weather, but it is very prone to studded tire wear.

The wear rates for WSDOT PCC pavement on both Interstate 5 in Seattle and

Interstate 90 in Spokane are about the same (0.03 inches per million studded tire passes).

In Spokane, a portion of PCC on Interstate 90 was ground in 1995 to eliminate wear of

about 1.25 inches in the wheelpaths. These wear depths are more extreme in Spokane than

Seattle because of the substantially higher studded tire usage rates in Eastern Washington.

Wear rate measurements were taken on SR 395 (south of Ritzville, Wash.) during

August 1998. The measurements were intended to evaluate the surface wear in the

wheelpaths, and specifically the tining grooves, attributable to studded tires. Because of

experimental features built into these sections, different levels of PCC strength were

incorporated into the original construction. For these three-year-old sections, the calculated

wear rates ranged from a low of 0.02 in. per million passes to a high of 0.10 in. per million.

However, these wear rates are likely high because tine grooves are more readily worn than

the “flat” PCC surface.

How bad is the pavement wear problem? WSDOT uses the guideline that any

pavement with rutting greater than 1/3 in. (9 mm) requires rehabilitation. The primary

reason for this criterion is to reduce the potential for hydroplaning accidents. On the basis

of measurements taken in 1998, about 8.0 percent of the WSDOT route system had ruts

and wear depths of greater than 1/3 in. This amounts to about 1,400 lane-miles out of a

total of 18,000 lane-miles. WSDOT knows that a major portion of this rutting and wear is

due to studded tires because the width of the wheel track matches automobile tires. Rutting

caused by structural deformation related to truck and bus traffic has a wider wheel track.

xvi

OREGON LEGISLATION

As discussed earlier, the weight of the stud, along with other factors, has an effect on

pavement wear. This was recently recognized in Oregon and has resulted in legislation that

went into effect for the winter 1998 season. A brief review of what led to the Oregon

legislation is important. A review of other current western state laws pertaining to studded

tires (specifically, in Idaho, California, Utah, and Montana) did not reveal any attempt by

these states to define and mandate the use of lighter weight studs.

In 1995, Oregon passed legislation that limited the stud weight to 1.5 grams. This

was accomplished in Oregon Revised Statutes, Chapter 815, “Vehicle Equipment

Generally,” Paragraph 815.167. The revised paragraph read as follows:

“815.167 Prohibition on selling studs other than lightweight studs.

• A tire dealer may not sell a tire equipped with studs that are not lightweight studs.

• A tire dealer may not sell a stud other than a lightweight stud for installation in a tire.

As used in this section:

• ‘Lightweight stud’ means a stud that weighs no more than 1.5 grams and that isintended for installation and use in a vehicle tire; and

• ‘Tire dealer’ means a person engaged in a business, trade, occupation, activity orenterprise that sells, transfers, exchanges or barters tires or tire related products forconsideration.”

This law took effect on November 1, 1996, thus requiring these lighter studs for the winter

of 1996-1997.

Two problems arose with the new stud definition. First, it did not recognize that

different stud weights are required for different tire sizes. Second, the studded tires that

were used in Oregon in winter 1996-1997 that met this definition of “lightweight stud” did

not perform well. Why this occurred is unclear.

In response to the studded tire performance problems, the Oregon legislature

enacted a revised law that was signed by the governor in August 1997. The new law

contains two revisions that merit review. First, Paragraph 815.165 amends the allowable

xvii

usage dates for studded tires. The revised law reduces the allowable usage period by one

month (the former period, November 1 to April 30, was changed to November 1 to April 1).

Second, Paragraph 815.167 Subparagraph 3(a) was amended to read as follows:

“(3) As used in this section:

‘Lightweight stud’ means a stud that is recommended by the manufacturer of the tire for the

type and size of the tire and that:

• Weighs no more than 1.5 grams if the stud is size 14 or less;

• Weighs no more than 2.3 grams if the stud size is 15 or 16; or

• Weighs no more that 3.0 grams if the stud size is 17 or larger.”

1999 WASHINGTON STATE LAW REVISION

In April 1999, a revision to the Revised Code of Washington was passed. The

definition of “lightweight stud” was patterned after the Oregon 1997 definition. However,

a modest clarification regarding stud size was added. The use of Tire Stud Manufacturing

Institute (TSMI) designations clarifies for stud installers the allowable weight of a stud for a

given size of stud. The size of the stud is essentially dictated by the tire manufacturers,

since they create the holes in the tread rubber for installing the studs.

A new section was added to Title 46 RCW “Motor Vehicles,” Chapter 46.04,

“Definitions,” to read as follows:

“(1) ’Lightweight stud’ means a stud intended for installation and use in a vehicle tire. As

used in this title, this means a stud that is recommended by the manufacturer of the tire for

the type and size of the tire and that:

(1) Weighs no more than 1.5 grams if the stud conforms to Tire Stud ManufacturingInstitute (TSMI) stud size 14 or less;

(2) Weighs no more than 2.3 grams if the stud conforms to TSMI stud size 15 or 16;or

(3) Weighs no more than 3.0 grams if the stud conforms to TSMI stud size 17 orlarger.

A lightweight stud may contain any materials necessary to achieve the lighter weight.”

xviii

In addition, two new sections were added to Title 46 RCW “Motor Vehicles,”

Chapter 46.37, “Vehicle lighting and other equipment”:

“(2) Beginning January 1, 2000, a person offering to sell to a tire dealer conducting

business in the state of Washington, a metal flange or cleat intended for installation as a

stud in a vehicle tire shall certify that the studs are lightweight studs as defined in section 1

of this act. Certification must be accomplished by clearly marking the boxes or containers

used to ship and store studs with the designation "lightweight." This section does not apply

to tires or studs in a wholesaler's existing inventory as of January 1, 2000.

“(3) Beginning July 1, 2001, a person may not sell a studded tire or sell a stud for

installation in a tire unless the stud qualifies as a lightweight stud under section 1 of this

act.”

CONCLUSIONS AND RECOMMENDATIONS

Given the results of this literature review and the revisions to Washington State’s

law regarding studded tires, the following conclusions and recommendations are made:

• Washington State has a reasonable studded tire use period and at five months is in line

with other western states.

• Few states have fully banned studded tires (in fact, only two). It is reasonable for

Washington State to continue to allow their use but to attempt to reduce the pavement

wear associated with them; however, the impact of stud-worn pavements on traffic safety

has not been assessed in this study.

• Studded tires currently used in Washington state are less damaging to pavement

surfaces than those that were available during the 1960s and early 1970s. The evolution

of the studded tire clearly reveals this. Nationally available statistics suggest that studded

tire wear rates in the 1960s were as much as four to ten times higher than current wear

rates for both AC and PCC surfaces, although pavement wear rate statistics tend to be

xix

imprecise. However, with today’s traffic volumes, studded tire pavement wear is still

significant on WSDOT highways.

• The wear experienced by both asphalt concrete and portland cement concrete pavement

surfaces in Washington State is generally lower than the rates reported by other states.

However, this undoubtedly varies throughout our state because aggregate sources (and

associated hardness) vary.

• The change from 55 mph to 70 mph on our rural Interstate highways has potentially

increased pavement wear caused by studded tires by a factor of two. The influence that

high speed has on studded wear likely explains, in part, the modest studded tire wear

noted on slower city streets.

• A modest change in studded tire wear is significant for some pavement types. A 1- to 2-

year increase in pavement life due to reduced studded tire wear will be enough to allow

some pavements to achieve their intended structural life.

• Currently available winter tires enhance snow and ice traction (see Appendix B). It is not

unreasonable to speculate that these tires will likely reduce studded tire usage.

Considerations for future work include the following:

• Monitor the performance of the newer studless winter tires. Such information could

result in further legislative/code revisions.

• Monitor the performance of lighter weight studded tires (less than 1.1 grams) used

elsewhere.

• Examine PCC and AC mixes that are more stud-wear resistant. WSDOT paved a stone

mastic asphalt (SMA) mixture during the 1999 paving season. That type of mix will be

more resistant to stud wear than WSDOT Class A mixes. Experience from Sweden

suggests that the wear resistance of SMA mixes can be 40 percent more than

conventional, dense graded asphalt concrete mixes (see Appendix A).

1

1. INTRODUCTION


(WSDOT) proposed legislation to amend the Revised Code of Washington with respect

to studded tires. In April 1999, legislation was passed that changed Washington’s laws

regarding studded tire use. These legislative changes were intended to reduce pavement

wear on Washington state’s highway system caused by studded tires without losing the

safety benefits that tire studs offer.

From the time that studded tires were first introduced, the advantages,

disadvantages, and effects of studded tires on vehicles, drivers, and pavement systems

have been the object of research and controversy. A few states have chosen to ban the use

of studded tires altogether, while others, such as Oregon and now Washington, have

passed legislation that is intended to reduce the road wear impacts of studs.

One objective of this report is to present a brief history of the studded tire. The

report also explores the relationship between pavement wear and developments in

studded tires that have taken place over the past 40 years. This information will provide a

background that helps to support and explain the amendments to the Revised Code of

Washington regarding studded tires.

STUDY APPROACH

These objectives were accomplished through an extensive review of world-wide

literature covering research on studded tires—their evolution and their relationship to

pavement wear—most of which was conducted from 1966 through 1975. The study also

looked at new developments in studded tire features and their impacts on pavement wear.

2

The primary source of information on these recent developments is research within

Scandinavia.

This report does deals in a limited manner with studded tire performance.

REPORT ORGANIZATION

This report contains three primary chapters. Chapter 2 discusses tire studs,

including their composition, the history of their development and acceptance, and

historical and current laws and restrictions on their use. Chapter 3 covers pavement wear:

primary mechanisms of stud-related pavement wear, an overview of pavement wear

studies, and a comprehensive discussion of stud-related factors that affect pavement

wear. Chapter 4 discusses the use of tire studs in Washington State specifically, including

their impacts on the WSDOT route system, the Oregon legislation on which changes to

Washington’s laws were patterned, and the proposed and final changes to Washington

State law.

3

2. THE STUDDED TIRE: PAST TO PRESENT

TIRE STUD CHARACTERISTICS

Development and Stud Types

The studded tire concept can be traced as far back as the 1890s, when "metallic

cleats" were used in pneumatic tires. The purpose of these cleats was to increase the

wear resistance of the tires and provide better protection against damage while on the

rough gravel roads of that time. However, these cleats were not necessary for long

because of improvements in both roads and tires (Cantz 1972).

Tire studs consist of two primary parts. The outside part of the stud is called a

jacket or body, which is held in the tire tread rubber by a flange at the base. The

core/insert or pin is the element that protrudes beyond the tire surface and contacts the

pavement surface. Figure 1 is a diagram of a typical first generation tire stud that

consisted of a 0.094-in. (2.4 mm) diameter tungsten carbide pin (i.e., the insert), which

typically protruded 0.063 in. (1.6 mm) from its 0.188-in. (4.7 mm) diameter steel body

(i.e., the jacket) (Burnett 1966). This single-flanged tire stud design was adopted as the

basic design by most of the tire stud manufacturers.

The European and Scandinavian countries are credited with initially marketing the

tire stud to the driving public in the late 1950s. The core of the first tire studs consisted

of a small piece of tungsten carbide, which was about the thickness of a ten-penny nail

(0.128 inches (3.2 mm)), was approximately 0.313 inches (7.8 mm) long, and was held in

place with a "jacket." As a unit, it was referred to as a "winter tire stud" (Miller 1966).

Figure 2 shows the basic design of these tire studs (Cantz 1972).

4

FIGURE 1. First generation single-flange tire stud (Miller 1967).

FIGURE 2. First tire studs with tungsten carbide cores (Cantz 1972).

5

Until the use of tungsten carbide as the core material, all previous attempts to

develop anti-skid devices had been unsuccessful. The success of the tungsten carbide

core was the result of its being one of the hardest man-made materials available at that

time. When manufactured to the proper specifications, and under normal driving

conditions, it closely matched the wear rate of the rubber tire tread (Miller 1966).

The jackets that hold the carbide core in place have been designed in various sizes

and shapes and are manufactured from many different materials, such as low carbon

steel, plastic, brass, aluminum, and porcelain. The original flanges on the jacket body

numbered as many as four. A threaded shank similar to a screw was even used in place

of the basic flange design (Miller 1966), as shown in Figure 2. Figure 3 shows the results

of the initial research that led to a single-flange tire stud design, which was adopted by

most of the world’s tire-stud manufacturers by 1964 (Cantz 1972).

FIGURE 3. Cross-sectional view of single-flanged tire stud (Cantz 1972).

Although numerous types of tire studs have been tested throughout the years, as

of 1972, only a few had been successfully marketed and used commercially. A list of the

6

four basic types of tire studs available in 1972, along with a brief description of their

characteristics, are shown in Table 1.

TABLE 1. Stud type and basic characteristics as of 1972 (Krukar 1972).Stud Type Basic Characteristics

Type I “Controlled Protrusion Stud” • Carbide pin will move into stud body ifprotrusion is exceeded

• 18 percent lighter in weight thanconventional stud

• 5 percent smaller flange thanconventional stud

Type II “Perma-T-Gripper Stud” • Pin found in other studs has beenreplaced with relatively small tungstenCarbide chips in a soft bonding matrixenclosed in a steel jacket

• Designed to wear within 10 percent oftire wear, thus maintaining a protrusionof approximately 0.020 inches (0.5mm) or less.

Type III “Conventional Steel Stud” • Tungsten carbide pin• Stud protrusion will increase with tire

wearType IV “Finnstop Stud”* • Stud body made of lightweight metal or

plastic with a tungsten carbide pin• Stud can be adjusted close to the tread

rubber eliminating oscillation of thestud

• Pin angle contact varies little withspeed

• Air cushion can be left under stud toreduce stiffness (floating stud)

• Reduces heat build up between rubberand stud

*A plastic jacket stud.

7

Stud/Tire Interaction

During normal service, the stud is held in place within the tire by the rubber

around the stud, which exerts compression on the jacket (Miller 1967). Once the stud has

been inserted properly, the force required to pull the entire stud out of the tread is

reported to be about 90 pounds (400 Newtons). According to the literature, the

centrifugal force acting on the stud is less than 2 pounds (8.9 Newtons) when the tire is

traveling at 50 mph (81 kph) (Miller 1966).

Evidently, a settling action takes place during the initial life of the tire stud. That

is to say, the rubber begins to envelop the shape of the jacket. As shown by Figure 4, the

rubber merely bridges the distance from the flange to the shank of the tire stud

immediately after its insertion. The maximum ability to retain the stud in the tire is not

developed until the rubber around the stud completely envelops the jacket (Miller 1967).

Manufacturers recommend that before drivers subject the studded tire to severe

driving conditions, they drive 50 miles (81 kilometers) at speeds of less than 50 mph hour

(81 km/h) to allow the stud to seat itself in the tire properly and to ensure maximum

retention of the tire stud (Miller 1967).

Evolution: Change in Stud Length and Weight

Since tire studs were first introduced, the stud flange diameter and the hardness of

the tungsten carbide pin have both decreased with time to be more comparable with tire

tread wear performance (Brunette 1995). During the late 1960s and early 1970s softer

carbides were chosen to better match the wear rate of the tire surface rubber, which also

reduced the average tire stud protrusion length (Transportation Research Board 1995).

These improvements to the tire stud were driven by pavement wear studies that revealed

8

FIGURE 4. Tire stud before and after break-in-period (Miller 1967).

that stud protrusion length was a significant factor in pavement wear rates (Brunette

1995). Table 2 displays the changes in average tire stud protrusion from 1966 to 1972.

TABLE 2. Change of average tire stud pin protrusion by year (Cantz 1972).Year Stud Protrusion

(inches (mm))1966196719681969197019711972

0.087 (2.2)0.081 (2.0)0.076 (1.9)0.074 (1.9)0.068 (1.7)0.065 (1.6)0.045 (1.1)

Finnish, Swedish, and Norwegian stud technical data suggest that current stud pin

protrusion is about 1.2 mm (Unhola 1997).

9

Research to develop a new stud design was intensified by the tire stud industry as

the possibilities of a legal ban on the use of tire studs increased. A result was the

development and marketing, in 1972, of "second generation studs," which were designed

to control how much the pin protruded beyond the tire surface throughout the life of the

tire (Transportation Research Board 1975). This stud became known as the "Controlled

Protrusion" (CP) stud.

The CP stud was 18 percent lighter and the flange is 5 percent smaller than the

conventional stud. It was designed with a tapered pin, which is allowed to move back

into the stud jacket when the dynamic force reaches a critical level (Transportation

Research Board 1975). The dynamic force is determined partially by the vehicle speed,

but mostly by the tire stud protrusion length (Cantz 1972). This means that these studs

maintained a certain protrusion level almost independent from the wear resistance of the

carbide insert and the tire, as well as from driving conditions (Brunette 1995). The CP

stud is graphically displayed in comparison with the first generation (conventional) stud

in Figure 5.

The critical minimum force necessary to move the pin is determined by the

dimensions of the tapered pin and the shape and dimensions of the hole in the stud body.

The tire stud protrusion is determined by this pin movement (Cantz 1972). The average

pin protrusion for these types of studs ranged between 0.040 to 0.050 in. (1.0 to 1.3 mm)

in 1972 (Brunette 1995). At the time, this was approximately 30 percent less than the

average tire stud protrusion associated with conventional studs. Tests in 1972 showed

that the new CP studs reduced pavement wear by 40 to 50 percent.

10

FIGURE 5. Comparison between the CP tire stud and the conventional stud(Cantz 1972).

Another advantage of the CP stud is a reduction in heat caused by the impact of

the tire stud on the pavement (Cantz 1972). This means that the temperature between the

stud and the tire tread is lower, which in turn eliminates the degradation of the of the

rubber surrounding the stud (Brunette 1995). All of this provides better stud retention

capabilities.

The manufacturing of the CP stud was further improved in 1983, which resulted

in additional weight reduction and improved protrusion characteristics (Brunette 1995).

The researchers also determined that radial tires with improved CP studs reduced

pavement wear by as much as 75 percent of that previously recorded for bias tires with

old conventional studs installed (Brunette 1995). The literature search revealed that in

1992, only the CP stud was being used in the United States and that the number of studs

per tire generally ranged from 64 to 120 (Lundy 1992).

11

Research and development to improve tire studs by reducing stud weight,

increasing stud durability, and decreasing pavement wear has continued in the

Scandinavian countries. As an example, the Swedish National Road Administration

performed research to investigate the pavement wearing characteristics of two new

"lightweight" studs in 1992 (Brunette 1995). One of the lightweight studs tested

consisted of a plastic jacket weighing 0.7 grams (0.02 oz.), while the other stud consisted

of a lightweight metal jacket and weighed 0.95 grams (0.03 oz.). As a comparison, the

older conventional studs weighed approximately 2.3 grams (0.08 oz.), and the controlled

protrusion stud weighed 2.0 grams (0.07 oz.). The test results indicated that when

lightweight studs were used, pavement wear was reduced by 50 percent in comparison to

pavement wear caused by any of the early 2.3 gram (0.08 oz.) steel studs. The

differences in pavement wear between the two lightweight studs was small; however, the

lightweight metal studs produced less pavement wear than the plastic lightweight stud,

despite its heavier weight. In addition to the pavement wear results, these lightweight

studs also displayed durability and pin protrusion characteristics similar to those of the

controlled protrusion studs.

Clearly, the tire studs of today have evolved dramatically since they were first

introduced in the early 1960s. Specifically, two major elements that contribute to

pavement wear have been significantly improved. The average stud protrusion length has

decreased from 0.087 in. (2.2 mm) in 1966 to a range of 0.047 to 0.059 in. (1.2 to 1.5

mm) in today’s tire studs. This is close to a 40 percent decrease in protrusion length.

Another element that contributes to pavement wear is the average weight of the tire stud.

This has also decreased substantially since the original studs of the early 1960s. The

12

recent tire studs in Scandinavia (i.e., the lightweight studs) weigh about 1.1 grams (0.04

oz.) as opposed to the original conventional steel studs of the early 1960s, which weighed

about 2.3 grams (0.08 oz.). This change has resulted in studs that are about 50 percent

lighter today than what they were over three decades ago. However, the typical tire stud

for passenger cars in the United States currently weighs about 1.7 to 1.9 grams (0.06 to

0.07 oz.) [54], which is only about 22 percent lighter than the older conventional tire

studs.

In the United States, the size designation of the tire stud is based on a system

derived by the Tire Stud Manufacturing Institute (TSMI). Although TSMI no longer

exists, tire dealers in the United States still utilize its sizing scheme today. As an

illustration, a TSMI No. 12 stud means that the stud hole in the tire tread, is 12/32s or

0.375 in. (9.5 mm) deep. In Europe, the stud manufacturers use a different designation

system to describe a stud. As an example, a stud in Europe might have a designation of

"9-11-1," which means that the stud head diameter is 9 mm (0.354 in.), the length of the

stud is 11 mm (0.4330 in.), and the stud has one flange. This 9-11-1 stud is basically

equivalent to the TSMI No. 12. Overall, approximately 85 to 90 percent of the tire studs

currently sold within the United States are TSMI No. 11, 12, and 13, which are all used

with standard size passenger car tires (Wessel 1997).

MARKETING THE STUDDED TIRE

The single-flanged tire stud was first accepted and extensively used on

automobiles in the 1961-1962 winter season in Europe, primarily in the Scandinavian

countries (Rosenthal et al 1969). This strong consumer acceptance during the studded

tires’ first season was encouraging to tire stud manufacturers. By 1962, studded tires

13

composed up to 50 percent of the winter tire market in several Scandinavian countries

(Miller 1966).

Given the favorable acceptance of the studded tire in the European countries, the

North American market was a natural progression for various manufacturers.

The tire industry in Canada established a test market in the winter season of 1963-

1964. An estimated 1.5 million tire studs were sold during that winter season. The

following year, 6 million were sold, and by the end of the 1965-1966 winter season,

Canadian sales of tire studs were estimated at over 25 million (Miller 1966).

A limited test market was established in the United States during the 1963-1964

winter season. One of the first tire studs to be marketed in the United States consisted of a

tungsten carbide insert with a bell-shaped plastic casing, called the Keinas-Hokken.

However, the method of inserting these studs into the tires was an issue (Miller 1966).

The Keinas-Hokken was quickly replaced by an improved version made by the Scason

Corporation, a European manufacturer. This new version allowed a more refined method

of insertion.

As marketing plans for the improved stud were being prepared, marketers

discovered that numerous states had laws on their books that read, "Any block, stud,

flange, cleat or any other protuberance of any material other than rubber which projects

beyond the tread will be illegal…" Because of those legal constraints, the initial 1963-

1964 test market was confined to just two or three states, and little was learned about the

market’s potential.

During the 1964-1965 winter season 13 states were thought to allow the use of

studded tires. These states were Connecticut, Kentucky, Maine, Maryland,

14

Massachusetts, Missouri, Nevada, New Hampshire, New York, Ohio, Oklahoma,

Tennessee, and Vermont (Miller 1966).

By the end of the 1965-1966 winter season, more than 30 states permitted the use

of studded tires, while some 18 states considered their use illegal. This rapid increase in

studded tire use in the first three seasons of their sale in the United States is summarized

in Table 3 (Transportation Research Board 1975).

TABLE 3. Increase in use of studded tires during the initial U.S. marketing period(1963–1966) (Transportation Research Board 1975).

WinterSeason

No. LegalStates

No. of StatesMarketed

No. of Tire StudsSold in USA

(millions)

Approximate No.of Tires

(100 studs/tire)1963-1964 13 2 – 3 3 – 5 30,0001964-1965 13 13 25 – 30 250,0001965-1966 28 28 250 – 275+ 2,500,000

Evidence that consumers were increasingly accepting of studded tires continued

to grow, and marketers estimated that an excess of half-a-billion studs would be sold

during the 1966-1967 winter season (Transportation Research Board 1975). Figure 6

shows the states, except for Alaska, in which studded tires were allowed by the end of the

1966-1967 winter season (Miller 1967).

During the period of 1965 to 1969, annual sales of studded tires increased

threefold, with total sales estimated to be around $830 million in 1969 (Roberts 1973).

These estimates implied wide-spread, popular acceptance of studded tires as a winter

driving aid by a significant proportion of vehicle owners in the northern states of this

country where their use was legal at that time. Sales of studded tires may have been as

high as 25 to 50 percent of the total snow-tire shipments during the 1969–1970 winter

season (Roberts 1973). This high level of use and acceptance by the general public had

15

come about despite the numerous legitimate questions that had been raised regarding the

performance of studded tires and their effect on pavement wear (Rosenthal et al 1969).

FIGURE 6. States (shaded), which allowed studded tires as of January 1, 1967(Miller 1967).

STUDDED TIRE USAGE RATES

According to the literature review, the current actual usage rates of studded tires

are generally unknown in the United States and Canada (Lundy 1992). The last time data

were collected regarding the percentage of vehicles in North America with studded tires

was in November 1972, when a questionnaire requesting use estimates was sent to the 45

states that allowed studded tires at that time, as well as to the Canadian provinces and

Scandinavian countries. The five states that did not allow the use of studded tires in 1972

were Hawaii, Louisiana, Minnesota, Mississippi, and Utah. Although annual sales

estimates demonstrated the studded tire’s continuing popularity, highway engineers and

16

administrators wanted to know the total number of vehicles in North America with

studded tires (Roberts 1973).

Estimates of studded tire use were reported as a percentage of registered

passenger cars by 37 states. Of these 37 states, seven reported studded tire use at not

more than 5 percent, with the remaining 30 states estimating usage within the range of 6

to 61 percent. These data were presumed to indicate the status of studded tire use in the

United States in 1972 north of the 37th parallel, excluding Minnesota and Utah (Roberts

1973). The collected data on the percentage of vehicles in the United States, Canada, and

abroad with studded tires are shown in Table 4 (Transportation Research Board 1975).

In general, the data showed that Sweden and Finland had higher rates of studded

tire use than most North American states and provinces in 1972. Evidently, Finland was

the only country that compared truck and car use at the time the data were collected

(Lundy 1992). The data also showed that the use of tire studs ranged from 0 to

approximately 75 percent of all vehicles, with areas of harsh winters experiencing ranges

from about 20 to 75 percent.

LAWS AND RESTRICTIONS FOR STUDDED TIRE USE

Since studded tires were introduced in the early 1960s, the decision to allow their

use in the United States has continuously evolved. In 1963 only 13 states permitted the

use of tire studs. An estimated 28 states had legalized their use by 1965, and by the end of

the 1966–1967 winter season, 34 states had legalized the use of tire studs.

A great deal of research was performed from 1965 to 1967 on the effects of

studded tires on highway pavements. As a result, the trend to legalize the use of studded

17

TABLE 4. Historical data on estimated percentage of studded tire use in 1972(Transportation Research Board 1975).

Country Agency % of Vehicleswith Studs

Agency % of Vehicleswith Studs

United States Alabama

AlaskaArizonaArkansasCaliforniaColoradoConnecticutDelawareFloridaGeorgiaHawaiiIdahoIllinoisIndianaIowaKansasKentuckyLouisianaMaineMarylandMassachusettsMichiganMinnesotaMississippiMissouri

1

6111

NA302518NANANL27121025712NLNANA3212NLNL14

MontanaNebraskaNevadaNew HampshireNew JerseyNew MexicoNew YorkNorth CarolinaNorth DakotaOhioOklahomaOregonPennsylvaniaRhode IslandSouth CarolinaSouth DakotaTennesseeTexasUtahVermontVirginiaWashingtonWest VirginiaWisconsinWyoming

60

3863020NA302322011028NA340NA0

NL601035102035

Canada Ontario

ManitobaQuebecMaritime ProvincesOttawa

32

20 – 2550

50+48

Finland Cars

Trucks

90 – 95

40

Sweden 60

NA = estimate not available

NL = not legal

18

tires reversed by 1974, with tire studs being legal (without restrictions) in only 16 states,

and permitted in 29 states (with restrictions) as well as the District of Columbia. Only

five states actually prohibited the use of studded tires (Transportation Research Board

1975). Figure 7 shows the results of a 1975 survey by the Transportation Research Board

that indicated the months during which studded tire use was restricted in the United

States and Canada.

a) No restrictions: AlabamaColoradoGeorgiaKentucky

MissouriNevadaNew HampshireNew Mexico

North CarolinaSouth CarolinaNorth DakotaTennessee

VermontWyomingAlbertaSaskatchewan

b) Restricted to period Shown:

Aug September October November Dec Jan Feb March April May June

15 Sep Alaska (except specified cities)

1 Oct Idaho, Nebraska

1 Oct British Columbia, Manitoba

1 Oct Arizona, Indiana, Maine

1 Oct Montana, Prince Edward Island

15 Oct Utah

15 Oct Del, D.C., MD, ND, VA, N. Scotia, Quebec

15 Oct Connecticut

15 Oct New York

16 Oct New Brunswick

31 Oct Rhode Island

1 Nov Iowa, OK, WA, W. Va.

1 Nov Kansas, Ohio

1 Nov Oregon, Pennsylvania, Newfoundland

2 Nov Massachusetts

15 Nov Arkansas

15 Nov Mich., New Jersey

c) Prohibited:

CaliforniaFloridaHawaiiIllinois

LouisianaMinnesota **Mississippi

TexasWisconsin **Ontario

** Limited use by out-of-state motorists permitted

FIGURE 7. Legal restrictions on use of studded tires in 1975 (Transportation ResearchBoard 1975).

19

The 1975 survey remained one of the only complete listings of restrictions on

studded tire use in the United States and Canadian provinces until 1990, when the

Alaskan Department of Transportation and Public Facilities conducted a similar survey

(Lundy 1992). The survey was sent to 30 highway agencies in the United States and 11

Canadian provinces and territories, as well as Finland, Norway, Sweden, and the former

West Germany. The results of this survey are shown in Table 5.

TABLE 5. 1990 Restrictions on use of studded tires (Lundy 1992).United States/Canadaa) No restrictions Colorado

VermontSaskatchewan

Note: Several other states outside the snow zonewere not surveyed. These states may or may notrestrict the use of studs.

b) Restricted to timeperiod shown

Alaska

ConnecticutIowaKansasMaineNevadaNew JerseyNew YorkRhode IslandUtah

(September 15 – April 30 (north of latitude 60° N)(October 1 – April 14 (south of latitude 60° N)(November 15 – April 30)(November 1 – April 1)(November 1 – April 5)(October 1 – May 1)(October 1 – April 30)(November 1 – April 1)(October 15 – May 1)(November 15 – April 1)(October 15 – March 15)

c) Restricted (periodunreported)

CaliforniaDelawareIdahoIndianaMontanaNebraska

North DakotaOregonPennsylvaniaSouth DakotaWashingtonWyoming

New BrunswickNova ScotiaQuebec

d) Prohibited ArizonaIllinoisMaryland

MichiganMinnesota

AlbertaNorthwest TerritoriesOntario

Northern Europea) No restrictionsb) Restricted Norway

SwedenFinland

(Period unreported)(31 October to Easter)(1 November to 31 March)

c) Prohibited Germany

20

A comparison of the results of this 1990 survey with the 1975 data (Figure 7)

reveals the changes that occurred within that 15-year period. In 1975 Arizona, Maryland,

and Michigan permitted the use of studded tires during specific periods; however, the

1990 data show that the use of tire studs was later prohibited in these three states. One

state, California, changed its laws from completely prohibiting studs to permitting them,

although the months of use were unreported. The 1990 data show that minor changes

were made in the usage periods of states that restricted the use of studs to specific dates.

There was a tremendous change in the regions that originally had no restrictions. In

1975, 14 states and two provinces had no restrictions on the use of studded tires.

However, by 1990 only three agencies (two states and one province) had no restrictions.

This shift in restrictions is likely the result of extensive research that had been performed

in the mid-1960s and 1970s on the negative effects of studded tires on highway

pavements.

To determine whether any changes had occurred since the 1990 survey, another

survey was conducted in 1995 for the Oregon Department of Transportation (Brunette

1995). The survey was sent to 29 Northern states and 10 Canadian provinces to

determine whether policy or agency perceptions regarding studded tire use, and effects on

pavement wear, had changed much since the 1990 survey.

The response rate for the northern states was over 86 percent (25 responses out of

29 surveyed), and of the Canadian provinces, four of ten responded (40 percent). The

responses to questions regarding restrictions on the dates of studded tires use are shown

in Table 6.

21

TABLE 6. 1995 Restrictions on use of studded tires (Brunette 1995).Unites Statesa) No restrictions Wyoming Hwy Dept.b) Restricted to timeperiod shown

Alaska DOT

California DOTConnecticutIowa DOTKansas DOTMaine DOTMaryland DOTMichigan DOT*Minnesota DOT**Montana DOTNebraska Dept. of RdsNevada DOTNew Jersey DOTNew York DOTNorth Dakota DOTOregon DOTRhode Island DOTUtah DOTWashington DOT

(September 30 – May 1 (North of latitude 60° N)(October 1 – April 15 (South of latitude 60° N)(November 1 – April 1)(November 15 – April 30)(November 1 – April 1)(November – April )(October 1 – May 1)(November 15 – April 15)(November 15 – April 15)(November 15 – May 1)(October 15 – May 1)(November 1 – April 1)(October 1 – April 30)(November 1 – April 15)(October 16 – April 30)(November 15 – April 15)(November 1 – April 30)(November 15 – April 1)(October 15 – March 31)(November 1 – March 31)

c) Restricted (periodunreported)

Colorado DOTDelaware DOTIdaho Trans.

d) Prohibited Illinois DOTIndiana DOT

Canadian Provincesa) No restrictions Albertab) Restricted Manitoba

Nova ScotiaQuebec

(October 1 – April 30)(Period Unreported)(October 1 – April 15)

c) Prohibited* November 1 – May 1 in the Upper Peninsula and Northern Lower Peninsula.** Studs were banned in 1972, but reinstated for rural mail carriers (only) in 1994.

As with the comparison between the 1975 and 1990 surveys, these results

indicated that only minor changes had occurred in the usage dates of agencies that

restricted the use of studs to a specific period. Minnesota, which until 1994 had banned

the use of studded tires altogether, now permits their use, but only for rural mail carriers.

Wyoming changed from restricted use to no restrictions at all, while Indiana changed

from restricted use to prohibiting tire stud use completely. Two states—Maryland and

Michigan—also changed from completely prohibiting the use of tire studs to allowing

22

their use during a restricted time period. Out of the 20 states that responded to the

survey, over 50 percent allow studs for 5.0 to 5.5 months per year. The allowable period

typically starts on October 15 or November 1 and ends April 1 or April 15. The four

Canadian provinces that responded (Alberta, Manitoba, Nova Scotia, and Quebec)

currently allow the use of studded tires. One of these provinces, Alberta, changed from

prohibiting their use in 1990 to permitting their use with no restrictions.

Responses to other questions in the 1995 survey indicated that most of the states

and provinces surveyed perceive studded tire use to be lower than in the past.

Additionally, the results showed that winter studded tire use has dropped to less than 10

percent of all autos. It is also interesting to note that mixed responses were received

regarding agency perceptions of the effect of studded tires on pavement wear. Fifteen

respondents identified a concern for studded tire pavement damage, while only ten

respondents (seven states and three providences) reported that they were not concerned.

The seven states were Colorado, Kansas, Maryland, Montana, New York, North Dakota,

and Wyoming.

23

3. PAVEMENT WEAR

MECHANISMS OF PAVEMENT WEAR

The results of the literature review showed that basically the abrasive action of the

stud against the road causes pavement wear. A report from Finland in 1978, summarized

in Table 7 (Brunette 1995), identified four main mechanisms by which studded tires

cause pavement wear. Given that no studies have been published that definitively

establish which cause has the greatest impact, the debate continues over which

mechanism is most important. The current belief in Alaska is that the primary stud-

related mechanism of asphalt surfaced pavement wear is scraping of the asphalt mastic

and subsequent abrasion of the aggregate (Brunette 1995, Lundy 1992).

TABLE 7. Mechanisms of pavement wear under studded tires (Lundy 1992).Cause Description1 The scraping action of the stud produces marks of wear on the asphalt

mastic formed by the binder and the fine-grained aggregate.2 The aggregate works loose from the pavement surface as a result of

scraping by studs.3 Scraping of the stud produces marks of wear on stone. Only in very soft

aggregate does a rock fragment wear away completely by this action.4 A stone is smashed by the impact of a stud and the pieces are loosened by

the scraping action of the stud.

PAVEMENT WEAR STUDIES

Early Indications

Most of what is known about studded tire use and its effects on pavements in

North America was recorded during the late 1960s to the mid-1970s. This surge of

research coincided with the use of conventional steel studs (i.e., the first generation stud).

24

Some states within the U.S. performed their own research independently, while other

states co-authored studies with bordering states.

These studies were undertaken to determine the amount of damage that might be

done to highway pavements by vehicles equipped with studded tires. Many of the early

research studies were carried out in the field as well as in the laboratory. However,

researchers later determined that the end result was often a lack of correlation between

the two study approaches (Brunette 1995, Transportation Research Board 1975).

Early (1965) field studies showed significant pavement wear from studded tires.

However, because time limitations required researchers to obtain general information as

quickly as possible, no provisions were made to gather quantitative measurements of

pavement wear damage (Jensen 1966). Therefore, the results were qualitative

(Transportation Research Board 1975).

These initial studies also indicated that wear was less severe on portland cement

concrete pavements than on the bituminous pavements, and that most of the damage

could be expected in areas where vehicles braked or accelerated (e.g., intersections,

curves, and tollgate lanes) (Jensen 1966). The limited preliminary testing did not show

any visual evidence of damage from constant-speed traffic.

On the basis of these 1965 tests, policy makers decided that the evidence that

serious widespread pavement damage could result from the use of studded tires was not

enough to withhold from the traveling public the potential safety benefits tire studs would

provide (Jensen 1966). They recognized, however, that additional data were needed.

Laboratory studies performed in 1975, along with field measurements of actual

pavement wear, confirmed the earlier findings. Unlike the previous studies, researchers

25

were able to give quantitative values to wear rates in terms of inches of wear per million

studded tire passes (Transportation Research Board 1975). Many of the laboratory test

programs used special traffic simulators with circular test tracks. They were constructed

to test the wear of various types of pavements under different studded tire applications.

Unfortunately, the diameters of these circular test tracks were typically not sufficient to

prevent stud scrubbing action, which resulted in minimal direct correlation to actual

traffic situations (Brunette 1995).

Overall, the number of pavement wear studies was limited. However, the

literature review yielded some basic information regarding tests on pavement wear.

Table 8 summarizes the results of tests performed in 1966 and 1967 on pavement surface

wear compiled from six sources (Keyser 1970).

Minnesota Comparisons, 1972

One important study compared the effects of pavement wear after one year

without studded tires against wear during the previous six-year period with studs. After

six winters of legalized stud use in Minnesota (1965 to 1971), the 1971 legislature opted

not to legalize studded tires for the 1971–1973 biennium (Preus 1972). Since 1965, when

studs were legally introduced in Minnesota, the Minnesota Department of Highways

(MDOH) had been making field observations and taking measurements on pavement

surfaces to determine the degree of wear associated with the use of studs. It measured

wear at 83 sites around the state to obtain a representative sample of various pavements,

traffic volumes, and geographic locations (Preus 1972). The legislature’s action provided

a unique opportunity for the MDOH to record and compare data on pavement wear from

this period with data from winters when studs would not be allowed.

TABLE 8. Summary of tests ( 1966 and 1967) on wear of pavement surface by studded tires [Keyser 1970].Load (Kg (lb.)) StudsVehicle

FrontWheel

RearWheel

Total FrontWheel

RearWheel

TirePressure

(kPa)

Temp.(°C)

Speed(Km/hr)

(mph)

Geometry TrackWidth

(cm(in.))

Volumeof Wheel

Passes

ContactMode

PavementType

Wear(mm (in.))

White and Jenkins, 1966Pickup 585

(1,300)765

(1,700)2,700

(6,000)72 72 --- --- 24 – 32

(15 – 20)16 – 24

(10 – 15)

Straight

Curve,r =36 ft

30.5(12)

46 - 61(18 –24)

10,660

5,330

Normal

AccelerationDeceleration

BC

BCBC

6.3 (0.25)

2.8 (0.11)4.5 (0.18)

Burke and McKenzie, 1966Auto --- --- --- --- 52 --- --- --- --- --- 25 Rapid Start PCC 1.0 (0.04)

Tessier and Normand, 1967 *Auto --- --- --- 90 120 --- -18 to 4.4 88

(55)Straight 91

(36)33,500 Normal BC 1.7 (0.068)

Lee, Page, and DeCarra, 1966Truck

Auto

1,575(3,500)

180(400)

1,800 (2)(4,000)(2)

405(900)

10,350(23,000)

1,170(2,600)

110

104

110

104

---

---

-11 to 18

-8 to 19

64(40)

64(40)

Straight &Curved

Straight

76(30)

76(30)

10,000

10,000

Normal

Normal

BCPCC

BCPCC

2.2 (0.086)1.4 (0.054)

1.7 (0.068)0.45 (0.018)

Bellis and Dempster, 1966Auto 315

(1,400)315

(1,400)1,260

(2,800)50 – 32 50 – 32 207

(30 psi)--- 32 max

(20 max)Straight --- 4,990 Normal

acceleration

Abrupt stop

Emergencystop

BCPCC

BCPCC

BCPCC

0.65 (0.026)0.80 (0.032)

0.50 (0.02)0.25 (0.01)

1.4 (0.056)0.38 (0.015)

* Data are from Keyser (1970).BC = Bituminous ConcretePCC = Portland Cement Concrete

27

Pavement wear measurements were continued following the statewide ban on

studded tire use. In addition, MDOH established new test points on several new

pavement sections that had never been exposed to studded tire traffic. This allowed

pavement wear data to be collected during the winter of 1971–1972 from sites where

wear was induced by normal traffic with sand and salt applications but with virtually no

studded tires. A summary of the results from a number of typical measurement points is

shown in Table 9.

These data show clearly that after the 1971–1972 winter season, and with the ban

on tire studs in effect, pavement wear was reduced to virtually zero. Similarly, the report

indicated that the results were the same on other test points throughout the state. These

results confirmed the conclusions of previous MDOH studies that pavement wear in

Minnesota was unquestionably related to studded tire use (Preus 1972).

TABLE 9. Depth of pavement surface wear in Minnesota at typical test points (in.(mm)) (Preus 1972).

TP 6* TP 33** TP 32*** TP 83****WinterSeason Yearly Cumulative Yearly Cumulative Yearly Cumulative Yearly Cumulative1966-67

1967-68

1968-69

1969-70

1970-71

1971-72

0.04(1.0)

0.07(1.8)

0.07(1.8)

0.05(1.3)

0.05(1.3)

0.00(0.0)

0.04(1.0)

0.11(2.8)

0.18(4.6)

0.23(5.9)

0.28(7.2)

0.28(7.2)

0.09(2.3)

0.07(1.8)

0.06(1.5)

0.00(0.0)

0.09(2.3)

0.16(4.1)

0.22(5.6)

0.22(5.6)

0.10(2.5)

0.03(0.75)

0.07(1.8)

0.00(0.0)

0.10(2.5)

0.13(3.3)

0.20(5.1)

0.20(5.1)

0.08(2.0)

0.07(1.8)

0.01(0.25)

0.08(2.0)

0.15(3.8)

0.16(4.1)

*Test Point 6, portland cement concrete, gravel aggregate.**Test Point 33, portland cement concrete, limestone aggregate.***Test Point 32, asphaltic concrete, high type.****Test Point 83, bituminous, intermediate type.

28

Applicability and Comparability of Past Research

Table 10 summarizes some basic information on road wear studies. This

information was originally presented in a 1990 publication by Hicks, et al., but was

obtained for this literature review from Lundy, et al. (1992). The synthesis indicated

several things. First, reported wear rates, and the units used, varied considerably between

highway agencies. Differences in wear rates were probably due to differences in

materials and in percentages of vehicles with studded tires.

The information available about pavement wear from studded tires is not always

in the same format. Some researchers have described wear on the basis of average annual

daily traffic (AADT) while others have chosen to report wear in terms of a fixed number

of studded tire passes. Still other researchers have reported wear in terms of total number

of passes. More recently in Sweden (Carlsson 1995), pavement wear has been assigned a

weight in grams per vehicle per kilometer driven, and is called the SPS index for

pavements. SPS is a Swedish abbreviation for specific wear, and it indicates the actual

wear from a certain amount of traffic from studded tires during a particular measuring

period, usually one winter season. Although SPS is considered to be reliable for

forecasting total pavement wear in Sweden, it does not provide an exact picture of

pavement wear (Carlsson 1995). Nonetheless, the SPS index appears to be the reporting

method that most Scandinavian researchers now use when reporting information on

studded tire pavement wear (Brunette 1995).

The synthesis found in Lundy (1992) also indicated the following:

• Pavement type has a great effect on pavement wear. Asphalt surfaces wear at

a faster rate than portland cement concrete.

29

TABLE 10. Historical summary of road wear studies (Lundy 1992).Reference Rate of Wear

(in./passes)Average Rate in

in. (mm)/100,000 passes

a) Literature

Quebec 0.25/100,000 0.25 (6.3)Acceleration 0.36-0.44/100,000 0.40 (10.0)Deceleration 0.18-0.20/100,000 0.19 (4.8)

Quebec

Normal 0.11/100,000 0.11 (2.8)Germany 0.11/120,000 0.09 (2.3)Finland 0.15-0.2/10,000 AADT N/ASweden 0.5/40,000 AADT N/AMaryland 0.28-1.07/100,000 0.70 (17.5)Minnesota 1.5/4,000,000 0.04 (1.0)

Concrete 0.026/100,000 0.03 (0.8)OregonAsphalt 0.066/100,000 0.07 (1.8)

b) 1990 Survey

California 0.0005-0.0018/1000 0.12 (3.0)Connecticut 0.08/1,000,000 0.01 (0.3)Maryland 0.028-0.107/10,000 0.68 (17.3)New Jersey 0.05 per year for

5400 AADT per laneN/A

New York 0.009-0.016/yearPCC pavements0.022-0.025/yearACC pavements

N/A

N/A

Oregon 0.032/100,000 PCCpavements

0.073/100,000 ACCpavements

0.03 (0.8)

0.07 (1.8)

Norway SPS*AC = 25

Topeka** = 15Mastic stone = 10 – 15

PCC = 10

N/A

Sweden 35 grams/vehicle(4 studded tires)/km

driven

N/A

* SPS = g/cm (specific wear in grams worn out of the surfacing when a car with 4studded wheels drives a 1 km distance).** Topeka is a sand-rich hotmix.

30

• In areas of acceleration and deceleration, pavements wear increases

substantially.

Given all of the recent improvements that have been implemented in tire stud and

pavement mix designs, it should be noted that this information is not considered

representative of current tire stud wear. However, the information contained in Table 10

can be used in a general manner and as a reference for further studies in this area

(Brunette 1995). With the exception of Germany, where studded tires have been banned

since the 1974–1975 winter season, the European information in Table 10 is fairly recent

for those countries reported and reflects more up-to-date wear rates.

Brunette (1995) reported that studded tire wear rates from two different Oregon

pavement studies were about the same: 0.34 in. per million passes for AC surfaces and

0.008 in. per million passes for PCC surfaces. Data from Minnesota (as summarized by

Brunette) suggest PCC wear rates of 0.06 to 0.07 in. per million passes.

Alaska Study, 1990

In North America, no substantial information regarding studded tire pavement

wear had been published since the introduction of the improved controlled protrusion

stud (Brunette 1995). However, in 1990 the state of Alaska conducted research that

resulted in published wear rates for asphalt concrete (Lundy 1992). The wear rates are

given for three sites in Juneau, Alaska, and the results are summarized in Table 11. The

wear rate was calculated by dividing the maximum rut depth by the estimated number of

studded tire passes.

31

TABLE 11. Juneau pavement wear per million studded tire passes (Lundy 1992).Location Total Stud Passes by 4/91

(million)Wear Rate per Million

Passes (in. (mm))

Juneau – Douglas Bridge: On Bridge Before Bridge

5.375.37

0.148 (3.8)0.134 (3.4)

Douglas Road 3.87 0.122 (3.1)Mendenhall Loop 5.84 0.102 (2.6)

The rates of wear from this Alaskan study appear to be very consistent between

the three sites, and they are considerably smaller than those shown in Table 10. The data

collected at Douglas Bridge (before and on the bridge) show a consistency in wear rate,

which eliminates the possibility that subgrade deformation had contributed to the rutting

(Lundy 1992). Not surprisingly, the study reported that pavement wear from studded

tires is greater in the winter than in the summer. However, although studs are not

permitted during the summer season, about 10 percent of total wheel track wear was

estimated to be caused by studded tire use during the summer (Lundy 1992). Additional

research showed that the primary cause of this wear was from small, lightweight vehicles

equipped with studded tires (Brunette 1995). This was determined by measuring the

center-to-center distance between the wheel track wear paths, which ranged from 1.4 to

1.5 meters (56 to 58 in.), and these measurements coincide with small, lightweight

vehicles.

Continuing Research in Scandinavia

The Road Administration, Road Institute, and tire manufacturers of Norway,

Sweden, and Finland have continued to perform extensive research on studded tires and

their effects on pavement wear (Barter et al 1996). The Scandinavian countries

approached studded tire wear in three related ways. First, the countries began to pass

32

legislation that mandated the use of lightweight studs (studs that weigh less than 1.1

grams (0.04 oz)) (Barter et al 1996). The core of these studs is tungsten carbide steel, but

the jacket is made of plastic or lightweight aluminum oxide. All of this reduces

pavement wear rates by as much as 50 percent. Second, they began to use a Stone Mastic

Asphalt (SMA) concrete mix for surface courses; this mix contains up to 70 percent

coarse aggregate (Barter et al 1996). The use of SMA was found to reduce pavement

wear rates from 25 to 50 percent. Third, they started using a more durable aggregate that

resisted tire stud wear at a higher success rate than aggregates from the local material

sources. These harder aggregates consist of fine grained metamorphic and volcanic

rocks. The use of these more durable aggregates has reduced wear rates by a factor of

three to five in comparison to the previous aggregate source. Some tests with SMA

surfacing have also been conducted in Alaska as recently as 1996. The overall result has

been a 45 percent improvement in the pavement wear rate over conventional asphalt

concrete pavement mixes.

Aggregate quality is the critical parameter that is most important to the wear-

resistance of asphalt pavements to studded tires (Jacobson 1997). Today in Sweden, the

best pavements are about five times more wear-resistant than the pavements of the mid-

1980s and possibly up to ten times better than those built at the end of the 1960s

(Jacobson 1997).

Wear Trends

A review of previous data suggests that studded tire pavement wear rates are

significantly lower today than during the 1960s. Data from Keyser (1970), Lundy (1992),

and Brunette (1995) indicate that the wear rates for both AC and PCC pavement surfaces

33

have decreased by a factor of ten. Keyser’s data suggest wear rates of about 2.0 to 6.8 in.

per million passes (after scaling up the application rates) for AC pavements. This is about

ten times higher if the current Oregon value of 0.34 in. per million is used. A comparison

of current Oregon PCC rates to those reported by Minnesota in 1971 also results in a

factor of about ten.

FACTORS THAT AFFECT PAVEMENT WEAR

An excellent summary of the several factors that have been identified as affecting

pavement wear rate was first prepared in 1970 by Keyser (1970). Keyser originally

identified the characteristics for each factor (i.e., vehicle, tire, stud, pavement,

environment, and traffic) that affect the rate of pavement wear. Keyser also identified the

most important factors for bituminous pavement wear as wheel load, stud protrusion,

temperature, and humidity. Table 12 represents a slightly modified version of Keyser’s

original summary. This modified table is the result of Brunette’s newer work (1995),

which based the modification on recent research from Finland. This recent research

quantified the effects that each of the factors contributes to pavement wear and added to

the original list of characteristics for each factor (Brunette 1995). The modifications

included the effect that the type of tire (e.g., radial or bias ply), the stud flange diameter,

vehicle speed, and the weight of the stud have on pavement wear.

Pavement wear factors include vehicle, tire, and stud systems.

34

TABLE 12. Factors affecting pavement wear (Brunette 1995).Factor Component Characteristic

Vehicle, Tires,and Studs

Vehicle Type and weight Axial load Number of studded tires (front, rear) Speed

Tire Type (snow or regular, bias ply vs. radial) Pneumatic Pressure Age Configuration of studs Number of studs

Stud Type (material, shape) Protrusion length Flange diameter Weight Orientation of studs with respect to tire wear

Stud wear vs. tire wearPavement Geometry Cornering (curves, sharp turns)

Tangent Section Intersection Slope

Surfacingmaterial

Type and characteristics (bituminous mixtures,surface treatment, precoated aggregate, chipping.Portland cement, hardness)

AgeSurfacecondition

Surface texture and profile Icy Compacted snow (compactness) Sanded and salted icy surface Slush

Environment Humidity,Temperature

Wet, dry, humid

Traffic Volume Number of passes and compositionSpeedWheel track Width; Distribution of wheel loadsContactmode

Start (normal, abrupt) = spin Stop (normal, abrupt) = skid Acceleration (rate) = spin Deceleration (rate) = skid

35

Vehicle

The heavier the vehicle, the greater the pavement wear. Another important factor

is vehicle speed. In 1992, a Swedish study examined the effects of vehicle speed on

pavement wear and determined that increased speed caused an increase in stud dynamic

force, which directly affects the pavement systems and hence increases wear (Brunette

1995). These findings were confirmed by a 1992 study performed in Finland (Unhola

1997). The results of this study are presented in Table 13 with vehicle speed in

kilometers per hour (km/h) and pavement wear in cubic centimeters (cm3). These results

show that the recent increase of Interstate rural speed limits in the United States from 90

km/h (55 mph) to 113 km/h (70 mph) has increased the potential for studded tire

pavement wear by nearly a factor of two. That is to say, pavement wear could potentially

increase from 0.41 cm3 to 0.80 cm3 (0.025 to 0.049 in3) as a result of this higher speed.

TABLE 13. Pavement wear due to vehicle speed (Unhola 1997).Vehicle Speed(km/h (mph))

Pavement Wear(cm3 (in3))

50 (30)60 (37)70 (43)80 (50)90 (55)100 (62)110 (67)120 (74)

0.20 (0.012)0.23 (0.014)0.27 (0.016)0.32 (0.020)0.42 (0.026)0.56 (0.034)0.78 (0.048)1.19 (0.073)

In 1972, a study of pavement wear on a low speed (15 mph (24 km/h)) simulator

determined that no difference in pavement wear could be found in similar studs of

different weight. However, the researchers realized that the reason for this was the low

36

speed of the simulator. At a speed of 15 mph (24 km/h), the variation in the dynamic

force of studs with different weight against the pavement was negligible (Cantz 1972).

Tires

The performance characteristics of steel belted radials have proven to be superior

to those of bias ply tires, thus inducing less pavement wear when used with studs.

Studs

Several factors related to the studs themselves affect pavement wear.

Stud Flange Diameter

Stud flange diameter influences the rate of pavement wear because the force

exerted by the stud on the road surface is directly related to the diameter of the stud

flange. Studs with a small flange offer less resistance and are pushed back into the tire

during their contact with the road (Cantz 1972).

Number of Studs

The number of studs per tire has also been shown to be a significant factor in

wheel path rutting. The number of tire studs used per tire has ranged over the years from

50 to 500 or more (Miller 1966). The latter, of course, represents an extreme situation,

such as tires used in ice-racing. The number of studs per tire and road wear increase at a

linear rate (Cantz 1972).

Unlike in the United States, the number of studs per tire has been limited by most

of the countries throughout Scandinavia. The allowable number of studs by tire size as

determined by the Scandinavian Tire and Rim Organization (STRO) in 1997 is shown in

Table 14. In the United States, the number of studs used on modern studded tires ranges

37

from 64 to 120, dependent on the size of tire, with a typical average of approximately 100

studs (Brunette 1995).

TABLE 14. Allowable number of studs by tire size (Unhola 1997).Allowable Number of StudsTire Size

(in. (cm)) Finland Norway Sweden13 (33) 90 90 90

14 – 15 (35.6–38.1) 110 110 110> 15 (> 38.1) 130/PC*

150/CV**150 130/PC

150/CV*Passenger Cars**Commercial Vehicles

Stud Protrusion

The impact that stud protrusion length has on pavement wear has been recognized

as an important studded tire performance variable because of an almost linear relationship

between tire stud protrusion and dynamic force (Transportation Research Board 1975).

The protrusion length affects the energy absorbed by the pavement (Rosenthal et al

1969). Thus, as stud protrusion increases so does the increase in road wear (Cantz 1972).

In 1966, tire stud protrusion was generally 0.087 in. (2.2 mm). This decreased to

0.065 in. (1.7 mm) by 1971 (Cantz 1972), a reduction of 25 percent. The development of

the controlled protrusion stud in 1972 resulted in the possibility of average stud

protrusion lengths ranging from 0.045 to 0.050 in. (1.1 to 1.3 mm) (Brunette 1995).

Today, the typical stud protrusion length is more in the range of 0.047 to 0.059 in. (1.2 to

1.5 mm) (Brunette 1995), a reduction of almost 40 percent since the 1960s.

Stud Weight

According to reports from Finland, over the last 35 years the pavement wear rate

has decreased by a factor of four because of a reduction in the size and weight of the

38

studs. It is important to reduce the weight because of the kinetic energy that is

transferred at impact between the stud and the pavement (Barter 1996).

The Technical Research Center of Finland (VTT) has performed extensive work

in this area, which was recently summarized in a 1997 report (Unhola 1997). The results

of this report, which show how stud weight increases pavement wear, are presented in

Table 15 with stud weight in grams and pavement wear in cubic centimeters (cm3). A

comparison of lightweight studs, weighing approximately 1.0 grams (0.035 oz), to steel

studs weighing approximately 2.0 grams (0.07 oz) revealed that a reduction in stud

weight resulted in about one-half the wear.

Currently, the typical tire stud for approximately 85 to 90 percent of passenger

cars in the United States (e.g., TSMI No. 11, 12, and 13 studs) weighs about 1.7 to 1.9

grams (0.06 to 0.07 oz) (Wessel 1997). This means that the potential to reduce pavement

wear by adopting a 1.5-gram (0.05 oz) stud is about 12 to 13 percent. If some states

decided to adopt the 1.1-gram (0.04 oz) stud for passenger cars—the stud of choice in

Scandinavian countries—the potential to reduce pavement wear would be about 36

percent.

TABLE 15. Pavement wear due to stud weight (Unhola 1997).Stud Weight(grams (oz))

Pavement Wear(cm3 (in3))

1.0 (0.035)1.5 (0.053)2.0 (0.070)2.5 (0.088)3.0 (0.105)

0.25 (0.015)0.35 (0.021)0.45 (0.027)0.60 (0.037)0.80 (0.049)

39

Pavement

As mentioned earlier, the pavement system itself also influences the rate at which

studded tires cause pavement wear. The pavement community has known for some time

that portland cement concrete pavements are much more resistant to tire studs than

asphalt surfaced pavements. The geometry of the road also contributes to where

pavement wear occurs. As an example, tire stud wear on tangent (straight) sections of

highways is significantly less (Transportation Research Board 1975) than that observed

on sharp curves, where the studs tend to scrape the pavement and thus increase wear

(Brunette 1995). At areas where acceleration and deceleration occur, such as at

intersections, tire stud wear appears to be extremely concentrated. One study determined

that tire stud wear was 3.5 times greater at deceleration areas than at tangent sections

(Keyser 1970).

Not surprisingly, tire stud wear of pavements is influenced by the condition of the

pavement surface, that is whether it is wet or dry and whether ice or snow covers the

surface. Studies have demonstrated, and it seems obvious, that on snow and ice covered

pavements the use of tire studs will cause less pavement wear than on bare pavement

surfaces. However, what may be surprising is that a wet asphalt pavement is worn down

nearly twice as fast as a dry one (Brunette 1995). The effect of moisture and pavement

surface temperature on the development of tire stud rutting is graphically depicted in

Figure 8.

Temperature

Temperature can also influence the rate of studded tire pavement wear. Cook and

Krukar (Krukar and Cook 1972; Sorenson et al 1973) determined that the lowest wear

40

rate for asphalt pavements occurs at or near 0 º Celsius, with increases in pavement wear

rates at temperatures below and above Celsius is 0 º Celsius. The increase in pavement

wear with pavement temperatures below 0 º reportedly associated with an increase in tire

hardness and pavement stiffness (Lundy 1992). As the temperature of the asphalt

pavement decreases, pavement stiffness increases. With lower temperatures, the force

required to push the stud into the stiffer tire also increases (Krukar and Cook 1972;

Sorenson et al 1973) so that for given loading situation, more of the stud will protrude,

which results in higher stud forces. The possibility of increased wear rates is the result of

this combination of high stud forces and increased pavement brittleness (Krukar and

Cook 1972; Sorenson et al 1973). Note that the effect of temperatures on concrete

pavements is much different than that on asphalt pavements. The rate of wear from tire

studs decreases on concrete pavements as the temperature increases (Brunette 1995).

FIGURE 8. The effect of temperature and water on the wearing of pavements (Brunette1995).

41

4. STUDDED TIRES IN WASHINGTON STATE


(WSDOT) proposed legislation to amend the Revised Code of Washington with respect to

studded tires. In April 1999, legislation was passed that changed Washington’s laws

regarding studded tire use. These legislative changes were intended to reduce pavement wear

on Washington state’s highway system caused by studded tires without losing any of the

safety benefits that tire studs offer.

Below is an overview of the known impacts of studded tires on the WSDOT route

system, recent Oregon and legislation on which WSDOT modeled its proposed changes,

the suggested input for 1998 Washington State legislative action, and the outcome of the

winter 1999 legislative session.

STUDDED TIRE IMPACTS ON THE WSDOT ROUTE SYSTEM

Studded tires cause accelerated pavement damage, with some pavement surfaces

being more susceptible than others. For example, because of studded tires, the use of open

graded asphalt concrete (WSDOT Class D) wearing courses on high volume routes in

Washington has been virtually eliminated. This paving material was used to enhance

pavement friction and reduce splash and spray during wet weather but it is estimated to wear

at a rate of about 0.2 in. per million studded tire passes. This is based on wear and traffic

experienced during the 1990s on SR 520 (Evergreen Point Floating Bridge).

The surface texture built into all new PCC pavements is quickly worn away after two

to three winter seasons. This was particularly noticeable on the paving on SR 395 north of

the tri-cities. Wear rate measurements on SR 395 south of Ritzville, Wash., in August 1998

revealed values ranging from 0.02 to 0.10 in. per million passes of studded tires. (The

variation was largely due to different PCC strengths.) However, the noted wear was mostly

associated with the tine grooves, which exhibited higher wear rates than the “flat” PCC

42

surface. The surface texture (tine grooves) was generally worn away only three years after

construction.

The wear rates for WSDOT PCC pavement on both Interstate 5 in Seattle and

Interstate 90 in Spokane are about the same (0.03 inches per million studded tire passes).

In Spokane, a portion of PCC on Interstate 90 was ground in 1995 to eliminate wear in the

wheelpaths of about 1.25 in. These wear depths are more extreme in Spokane than Seattle

because of the substantially higher studded tire usage rates in Eastern Washington.

How bad is the pavement wear problem? WSDOT uses the guideline that any

pavement with rutting greater than 1/3 inch (9 mm) requires rehabilitation. The primary

reason for this criterion is to reduce the potential for hydroplaning accidents. On the basis

of measurements taken in 1998, about 8.0 percent of the WSDOT route system had ruts

and wear of greater than 1/3 inch. This amounts to about 1,400 lane-miles out of a total of

18,000 lane-miles. WSDOT knows that a major portion of this rutting and wear is due to

studded tires because the width of the wheel track matches automobiles tires. Rutting

caused by structural deformation related to truck and bus traffic has a wider wheel track.

Stud usage is an important factor in any discussion of state pavement wear. A

survey conducted by WSDOT during the winter of 1996-1997 revealed that, on average, 10

percent of passenger vehicles use studded tires in Western Washington and 32 percent in

Eastern Washington (the percentages are based on two studded tires per vehicle). The

surveys were taken in parking lots and garages at 14 locations. Of these locations, the

lowest stud usage was observed in Puyallup (6 percent) and the highest in Spokane (56

percent).

OREGON LEGISLATION

As discussed earlier in this report, the weight of the stud, along with other factors,

has an effect on pavement wear. This was recently recognized in Oregon and has resulted

in new legislation that went into effect for the winter 1998 season. A brief review of what

43

led to the Oregon legislation is important. A review of other current western state laws

pertaining to studded tires (specifically, in Idaho, California, Utah, and Montana) did not

reveal any attempt by these states to define and mandate the use of lighter weight studs.

In 1995, Oregon passed legislation that limited stud weight to no more than 1.5 g.

This was accomplished in Oregon Revised Statutes, Chapter 815, “Vehicle Equipment

Generally,” Paragraph 815.167. The revised paragraph read as follows:

“815.167 Prohibition on selling studs other than lightweight studs.

• A tire dealer may not sell a tire equipped with studs that are not lightweight studs.

• A tire dealer may not sell a stud other than a lightweight stud for installation in a tire.

As used in this section:

• ‘Lightweight stud’ means a stud that weighs no more than 1.5 grams and that isintended for installation and use in a vehicle tire; and

• ‘Tire dealer’ means a person engaged in a business, trade, occupation, activity orenterprise that sells, transfers, exchanges or barters tires or tire related products forconsideration.”

This law took effect on November 1, 1996, thus requiring these lighter studs for the winter

of 1996-1997.

Two problems arose with the new stud definition. First, it did not recognize that

different stud weights are required for different tire sizes. Second, the studs that were used

in Oregon in winter 1996-1997 that met this definition of “lightweight” did not perform

well. Why this occurred is unclear.

In response to the stud performance problems, the Oregon legislature enacted a

revised law that was signed by the governor in August 1997. The new law contains two

revisions that merit review. First, Paragraph 815.165 amends the allowable usage dates for

studded tires. The revised law reduces the allowable usage period by one month (the former

period, November 1 to April 30, was changed to November 1 to April 1). Second,

Paragraph 815.167 Subparagraph 3(a) was amended to read as follows:

“(3) As used in this section:

44

‘Lightweight stud’ means a stud that is recommended by the manufacturer of the tire for the

type and size of the tire and that:

• Weighs no more than 1.5 grams if the stud is size 14 or less;

• Weighs no more than 2.3 grams if the stud size is 15 or 16; or

• Weighs no more that 3.0 grams if the stud size is 17 or larger.”

PROPOSED WASHINGTON STATE LAW REVISION

The proposed WSDOT definition of “lightweight stud” is shown below and was

patterned after the Oregon 1997 definition. However, a modest clarification regarding stud

size was added.

In the United States, studs are sized according to the Tire Stud Manufacturing

Institute (TSMI). Although this institute no longer exists, its sizing scheme is still used by

tire dealers across the United States. To illustrate, a TSMI No. 12 stud means that the stud

hole in the tire tread is 12/32’s of an inch deep (or 9.525 mm). Similarly, a TSMI No. 17

stud would fit into a stud hole 17/32’s of an inch deep.

WSDOT proposed that a new section added to Title 46 RCW “Motor Vehicles,”

Chapter 46.04, “Definitions,” read as follows:

“’Lightweight stud’ means a stud intended for installation and use in a vehicle tire. As

used in this Section, this means a stud that is recommended by the manufacturer of the tire

for the type and size of the tire and that:

• Weighs no more than 1.5 grams if the stud conforms to (Tire Stud ManufacturingInstitute) TSMI Stud Size 14 or less;

• Weighs no more than 2.3 grams if the stud conforms to TSMI Stud Size 15 or 16;or

• Weighs no more than 3.0 grams if the stud conforms to TSMI Stud Size 17 orlarger.


45

The use of TSMI designations clarifies for stud installers the allowable weight of a

stud for a given size of stud. The size of the stud is essentially dictated by the tire

manufacturers, since they create the holes in the tread rubber for installing the studs.

1999 WASHINGTON STATE LAW REVISION

The proposed revisions did not pass during the 1997-1998 legislative session.

However, in April 1999, a revision to the Revised Code of Washington was passed.

A new section was added to Title 46 RCW “Motor Vehicles,” Chapter 46.04,

“Definitions,” to read as follows:

“(1) ’Lightweight stud’ means a stud intended for installation and use in a vehicle tire. As

used in this title, this means a stud that is recommended by the manufacturer of the tire for

the type and size of the tire and that:

(1) Weighs no more than 1.5 grams if the stud conforms to Tire Stud ManufacturingInstitute (TSMI) stud size 14 or less;

(2) Weighs no more than 2.3 grams if the stud conforms to TSMI stud size 15 or 16;or

(3) Weighs no more than 3.0 grams if the stud conforms to TSMI stud size 17 orlarger.


In addition, two new sections were added to Title 46 RCW “Motor Vehicles,”

Chapter 46.37, “Vehicle lighting and other equipment”:

“(2) Beginning January 1, 2000, a person offering to sell to a tire dealer conducting

business in the state of Washington, a metal flange or cleat intended for installation as a

stud in a vehicle tire shall certify that the studs are lightweight studs as defined in section 1

of this act. Certification must be accomplished by clearly marking the boxes or containers

used to ship and store studs with the designation "lightweight." This section does not apply

to tires or studs in a wholesaler's existing inventory as of January 1, 2000.

46

“(3) Beginning July 1, 2001, a person may not sell a studded tire or sell a stud for

installation in a tire unless the stud qualifies as a lightweight stud under section 1 of this

act.”

CONCLUSIONS AND RECOMMENDATIONS

Given the results of this literature review and the revisions to Washington State’s

law regarding studded tires, the following conclusions and recommendations are made:

• Washington State has a reasonable studded tire use period and at five months is in line

with other western states.

• Few states have fully banned studded tires (in fact, only two). It is reasonable to attempt

to reduce the pavement wear associated with them; however, the impact of stud-worn

pavements on traffic safety has not been assessed in this study.

• Studded tires currently used in Washington state are less damaging to pavement

surfaces than those that were available during the 1960s and early 1970s. The evolution

of the studded tire clearly reveals this. Nationally available statistics suggest that studded

tire wear rates in the 1960s were as much as four to ten times higher than current wear

rates for both AC and PCC surfaces, although pavement wear rate statistics tend to be

imprecise. However, with today’s traffic volumes, studded tire pavement wear is still

significant on WSDOT highways.

• The wear experienced by both asphalt concrete and portland cement concrete pavement

surfaces in Washington State is generally lower than the rates reported by other states.

However, this undoubtedly varies throughout our state because aggregate sources (and

associated hardness) vary.

• The change from 55 mph to 70 mph on our rural Interstate highways has potentially

increased pavement wear caused by studded tires by a factor of two. The influence that

high speed has on studded wear likely explains, in part, the modest studded tire wear

noted on slower city streets.

47

• A modest change in studded tire wear is significant for some pavement types. A 1- to 2-

year increase in pavement life due to a reduction in studded tire wear will allow some

pavements to achieve their intended structural life.

• Currently available winter tires enhance snow and ice traction (see Appendix B). It is not

unreasonable to speculate that these tires will likely reduce studded tire usage.

• WSDOT Class D open graded asphalt mixes are highly susceptible to studded tire

wear. These mixes reduce splash and spray caused by water and traffic and provide a

high level of surface friction. However, currently WSDOT rarely uses these mixes

because of studded tire wear effects.

Considerations for future work include the following:

• Monitor the performance of the newer studless winter tires. Such information could

result in further legislative/code revisions.

• Monitor the performance of lighter weight studded tires (less than 1.1 grams) used

elsewhere.

• Examine PCC and AC mixes that are more stud-wear resistant. WSDOT paved a stone

mastic asphalt (SMA) mixture during the 1999 paving season. That type of mix will be

more resistant to stud wear than WSDOT Class A mixes. Experience from Sweden

suggests that the wear resistance of SMA mixes can be 40 percent more than

conventional, dense graded asphalt concrete mixes (see Appendix A).

48

REFERENCES

Barter, T.D., Johnson, E.G., and Sterley, D.M., “Options for Reducing Stud-RelatedPavement Wear,” Alaska Department of Transportation and Public Facilities,September 1996.

Bellis, W. R., and Dempster, Jr, J. T., “Studded Tire Evaluation in New Jersey,” HighwayResearch Board, Highway Research Record, No. 171, January 1967.

Brunette, B.E., “The Use and Effects of Studded Tires on Oregon Pavements,” M. S.Thesis, Oregon State University, Corvallis, 1995.

Burnett, W. B., and Kearney, E. J. “Studded Tires – Skid Resistance and PavementDamage,” Highway Research Board, Highway Research Record, No. 136, 1966.

Cantz, R., “New Tire-Stud Developments,” Highway Research Board, Highway ResearchRecord, No. 418, 1972.

Carlsson, A., Centrell, P., and Oberg, G., “Studded Tyres—Socio-economiccalculations,” Swedish Road and Transport Research Institute, No. 756A, 1995.

Jacobson, T., “The wear resistance of bituminous mixture to studded tyres—the Swedishexperience,” The Swedish National Road and Transport Research Institute(VTI), No. 30, 1997.

Jensen, P. A. and Korfhage, G. R., “Preliminary Studies of Effect of Studded Tires onHighway Pavements,” Highway Research Board, Highway Research Record,No.136, 1966.

Keyser, J. H., “Effect of Studded Tires on the Durability of Road Surfacing,” EcolePolytechnique, Montreal, Canada, 38 pp., January, 1970, and Highway ResearchBoard, Highway Research Record, No. 331, 1970.

Krukar, M., and Cook, J. C., “Studded Tire Pavement Wear Reduction & Repair—PhaseI,” Washington State Highway Department Research Program Report 9.1,(Transportation Systems Section Publication H-39), Washington State University;Pullman, Washington, December 30, 1972.

Krukar, M., and Cook, J. C., “The Effect of Studded Tires on Different PavementMaterials and Surface Textures,” (Transportation Systems Section Publication H-36), Washington State University, Pullman, Washington, July 1972.

Lundy, J.R., Hicks, R.G., Scholz, T.V., and Esch, D.C., “Wheel Track Rutting Dueto Studded Tires,” Transportation Research Record, No. 1348, 1992.

49

Malik, M., “Preliminary Estimates for 1993 Studded Tire Pavement Damage,” OregonDepartment of Transportation, Financial Services Branch, Economic andFinancial Analysis Unit, September 1994.

Miller, II, W. P., “The Winter Tire Stud,” Highway Research Board, Highway ResearchRecord, No. 136, 1966.

Miller, II, W. P., “Principles of Winter Tire Studs,” Highway Research Board, HighwayResearch Record, No. 171, 1967.

Preus, C.K., “Studded Tire Effects on Pavements and Traffic Safety in Minnesota,”Minnesota Department of Highways, Highway Research Board, Highway

Research Record, No. 418, 1972.

Roberts, S. E., “Use of Studded Tires in the United States,” Highway Research Board,Highway Research Record, No.477, 1973.

Rosenthal, P., Haselton, F. R., Bird, K. D., and Joseph, P. J., “Evaluation of StuddedTires: Performance Data and Pavement Wear Measurement,” CornellAeronautical Laboratory, Transportation Research Board, NCHRP Report No.61,1969.

Smith, R. W. and Clough, D.J., “Effectiveness of Tires Under Winter DrivingConditions,” Highway Research Board, Highway Research Record, No.418,1972.

Sorenson, H. C., Krukar, M., and Cook, J. C., “Studded Tire Pavement Wear Reduction& Repair – Phase III,” Washington State Highway Department Research ProgramReport 9.3, (Transportation Systems Section Publication H-41), Washington StateUniversity; Pullman, Washington, December 31, 1973.

Transportation Research Board, “Effects of Studded Tires,” NCHRP Synthesis ofPractice 32, 1975

Unhola, T., “Studded Tires the Finish Way,” Technical Research Centre of Finland,Communities and Infrastructure, 1997.

Wessel, B., Memorandum: Information on Studded Tire Regulations, Stud Sizes, andStud Weights, Bruno Wessel, Inc., November 1997.

Washington State Pavement Management System (1996 and 1997 versions), WashingtonState Department of Transportation.

50

BIBLIOGRAPHY

American Concrete Paving Association, Technical Subcommittee on SurfaceProperties, “Facts about Studded Tires,” Technical Bulletin No. 18, August 1974.

Brunette, B.E., and Lundy, J.R., “Use and Effect of Studded Tires on OregonPavements,” Transportation Research Record, No. 1536, 1996.

Burke, John F. and McKenzie, L. J., “Some Tests of Studded Tires in Illinois,”Highway Research Board, Highway Research Record, No. 136, January 1966.

Carlsson A., and Oberg, G., “Winter Tyres – Effects of Proposed Rules,” SwedishRoadand Transport Research Institute, No. 757A, 1995.

Cook, J.C., “Reduction of Pavement Wear Caused by Studded Tires,” WashingtonState University, College of Engineering Research Division, Highway ResearchSection, April 1971.

Cook, J. C., and Krukar, M., “The Effect of Third Generation Tire Studs onPavement Wear Reduction,” 1977–1979. Report of Test Results on PavementWear from Various Tire-Stud Combinations, Washington State University, ReportNo. 79/15-27, June 1979

Creswell, J. S., Dunlap, D. F., and Green, J. A., “Studded Tires and Highway Safety -Feasibility of Determining Indirect Benefits,” Transportation Research Board,NCHRP Report, No. 176, 1977.

Federal Highway Administration, “Studded Tires – An Update,” Pavement Branch,January 1983.

Gustafson, K., “Pavement Wear from Studded Tires – the Swedish Solution,”Swedish National Road and Transport Research Institute (VTI), 1997.

Jacobson, T., “Study of wear resistance of bituminous mixes to studded tyres – Testswith slabs of bituminous mixes inserted in roads and in the VTI’s road simulator,”Vag-och Trafik Institutet (VTI), No. 245, 1995.

Jacobson, T., “Wear resistance of bituminous mixes to studded tyres – A novelapproach to field measurement and correlation with VTI’s road simulator,”Vag-och Trafik Institutet (VTI), No. 193, 1993

Kallberg, V., Kanner, H., Makinen, T., and Roine, M., “Estimation of Effects ofReduced Salting and Deceased Use of Studded Tires on Road Accidents inWinter,” Transportation Research Record, No. 1533, 1996

51

Kennametal, Inc., “Studded Tires the Winter Winner,” February 1985.

Keyser, J. H., “Effect of Studded Tires on the Durability of Road Surfacing,” EcolePolytechnique, Montreal, Canada, 38 pp., January, 1970, and Highway ResearchBoard, Highway Research Record, No. 331, 1970.

Keyser, J. H., “Resistance of Various Types of Bituminous Concrete and CementConcrete to Wear by Studded Tires,” Highway Research Board, HighwayResearch Record, No. 352, 1971.

Keyser, J. H., “Mix Design Criteria for Wear-Resistant Bituminous PavementSurfaces,” Highway Research Board, Highway Research Record, No. 418, 1972.

Konagai, N., Asano, M., and Horita, N., “Influence of Regulation of Studded Tire Use inHokkaido, Japan,” Transportation Research Record, No. 1387, 1996.

Krukar, M., and Cook, J. C., “The Effect of Studded Tires on Various Pavements andSurfaces,” Highway Research Board, Highway Research Record, No.477, 1973.

Krukar, M., and Cook, J. C., “Studded Tire Pavement Wear Reduction & Repair –Phase II,” Washington State Highway Department Research Program Report 9.2,(Transportation Systems Section Publication H-40), Washington State University;Pullman, Washington, July, 1973.

Lee, A., Page, T. A. and DeCarrera, R., “Effects of Carbide Studded Tires onRoadway Surfaces,” Highway Research Board, Highway Research Record, No.136, 1966.

Leppanen, A., “Final Result of Road Traffic in Winter Project: Socioeconomic Effectsof Winter Maintenance and Studded Tires,” Transportation Research Record, No.1533, 1996.

Lu, J.J., “Vehicle Traction Performance on Snowy and Icy Surfaces,” TransportationResearch Record, No. 1536, 1996.

Lundy, J.R., Hicks, R.G., Scholz, T.V., and Esch, D.C., “Wheel Track Rutting DueTo Studded Tires,” Transportation Research Record, No. 1348, 1992.

Normand, J., “Influence of Studded Tires on Winter Driving Safety in Quebec,”Department of Roads, Quebec, Highway Research Board, Highway ResearchRecord, No. 352, 1971.

“Pavement Wear Due to Studded Tyres Run-over Wear Test,” Technical ResearchCentre of Finland, Road Engineering and Geotechnology, 1996.

52

Peterson, D. E., Blake, D. G., “A Synthesis on Studded Tires,” Materials and TestsDivision Utah State Department of Highway, January1973.

Preus, C.K., “After Studs in Minnesota,” Minnesota Department of Highways,Highway Research Board, Highway Research Record, No. 477, 1973.

Scandinavian Tire and Rim Organization, “Tyre Regulations in the Nordic Countries”1996.

Smith, R. W., Ewens, W. E., and Clough, D. J., “Effectiveness of Studded Tires,”Highway Research Board, Highway Research Record, No.352, 1971.

Smith, P., and Schonfeld, R., “Pavement Wear Due to Studded Tires and theEconomic Consequences in Ontario,” Report RR 152, Department of Highways,Ontario, Canada, November, 1969, and Highway Research Board, HighwayResearch Record, No. 331, 1970.

Smith, P., and Schonfeld, R., “Studies of Studded-Tire Damage and Performance inOntario During the Winter of 1969-70,”Highway Research Board, HighwayResearch Record, No. 352, 1971.

Transportation Research Board, “Effects of Studded Tires,” NCHRP Synthesis ofPractice 32, 1975

Washington State Department of Transportation, “Studded Tires,” Maintenance &Operations Group, ISCORD 97, January 1979.

Washington State Department of Transportation, “Studded Tires – An Update,”Pavement Branch, January 1983.

Washington State Highway Commission, “A Report on Studded Tires,” Departmentof Highways, 1971.

Wessel, B., Memorandum: Information on Studded Tire Regulations, Stud Sizes, andStud Weights, Bruno Wessel, Inc., November 1997.

White, O. A. and Jenkins, J. C., “Test of Steel Studded Snow Tires,” HighwayResearch Board, Highway Research Record, No. 136, 1966.

Whitehurst, E. A., and Easton, A. H., “An Evaluation of Studded Tire Performance,”Highway Research Board, Highway Research Record, No. 171, 1967.

APPENDICES

A-1

APPENDIX ANotable Items from the Scandinavian Tire and Rim Organization

1997 Winter Traffic Conference, Ivalo, Finland

The proceedings for the Winter Traffic Conference (March 18-21, 1997) provide

insights that merit notation. These include the following points made by various authors.

Anne Leppanen, “The Road Traffic in Winter Project”

• The grip quality of studded tires, even after 40,000 km of wear, was superior on ice in

comparison to studless winter tires. (Note: the definition of a “winter tire” was unclear

but probably included a broad range of winter tires than defined in Appendix B.)

• The durability of the best performing lightweight studs (1.1 g) was, in general, about the

same as that of conventional weight studs (1.8 g). However, the various stud

manufacturers reported significant variation in both stud durability and the ability of

studs to remain in tires.

• In Finland 95 percent of all passenger cars were equipped with studded tires during the

winter months.

• During the winter, frosty and icy road conditions were found 11 to 13 percent of the

time in coastal and central Finland. For northern Finland, those conditions were found

20 percent of the time. Wet road conditions existed about 46 to 49 percent of the time.

• Hard packed snow was worn away twice as fast by studded tires as by conventional

tires. For soft packed snow, the wear rates were about the same.

• Fuel consumption (as compared to dry, bare pavement)

- increased 15 percent for slippery, snowy, and uneven pavements

- increased 1.2 percent for studded tires in comparison to studless winter tires.

A-2

Finn Contact 3/95, Editor: Jarmo Ikonen

• Friction levels of 0.21 to 0.30 can be achieved on snow and ice by sanding. To achieve

higher friction levels, salting had to be used. Very slippery road surface conditions were

defined as having a friction value of below 0.20.

• A conclusion was drawn that the accident risk of drivers with unstudded winter tires was

higher than those with studded tires over a wide range of road surface conditions (again,

the precise definition of winter tires was unclear).

Anne Carlsson et al, “Studded Tyres”

• Lightweight studded tires produced, in general, 50 percent less pavement wear on both

SMA and dense, graded asphalt concrete. SMA mixes exhibited about 40 percent less

wear in comparison to traditional dense, graded asphalt concrete (as based on SPS

Index values).

• Japanese studies were quoted that showed a relationship between studded tire pavement

wear and particle content in the air and the lungs of humans and animals.

• Norwegian studies were quoted that have shown that inhalable particles can reach three

times the recommended limit.

Antero Juopperi, “Prohibition of Studded Winter Tyres in Japan”

• In Hokkaido and northern Honshu, studded tire use was essentially 100 percent by the

early 1970s.

• During the 1970s and 1980s, studded tire regulations attempted to reduce usage in order

to decrease suspended particulate matter.

• Currently, studded tire use is close to zero. This was achieved by 1992-1993.

• The consequences of banning studded tires included the following:

- Suspended particulate matter (mg/m3) decreased as studded tire use decreased.

- Pavement surface abrasion was reduced from 6 mm (0.24 in.) per year to 1 mm

(0.04 in.) per year.

A-3

- Following the studded tire ban, winter accident rates increased significantly.

- The elimination of studded tires resulted in slippery snow surface conditions.

Studded tires help to break up the crust of ice that forms on top of snow compacted

by vehicles.

Halvard Nilsson, “Winter Tyres in Scandinavia”

• Bias belted tires of the 1960s contributed to excessive studded tire pavement wear.

• By 1989, the use of radial tires, reduced stud protrusion, the fewer number of studs on a

tire, and improved pavement surfaces all led to a significant reduction in pavement wear.

• Finnish studies have shown that studded tires reduce fatal accidents by 48 percent on ice

and snow and by 20 percent over the whole winter period.

• The optimum protrusion of a stud above the tire surface is about 1.0 to 1.5 mm. If it is

less than 1.0 mm, the effect of the stud on the ice is too small; above 1.5 mm, the forces

on the stud are too high, causing excessive pavement wear.

• “Although many new tyre types have been introduced, no tyre has been able to match

the effect of studs on ice.”

• “Many inventors have tried to find new ideas for studs, in particular studs with a low

force against the road surface. These solutions usually incorporate moving parts, but

experience has shown that these are expensive and durability is often insufficient.”

B-1

APPENDIX BNew Technology Winter Tires

The M&S designation on many (if not most) passenger car tires implies that the tire

has a tread design that is beneficial in mud and snow conditions. However, a new type of

tire—termed a “winter tire”—has come on the scene. These winter tires have tread

composed of special rubber compounds and tread designs that enhance their performance in

snow and ice conditions. To recognize this new family of tires, the Rubber Manufacturers

Association will be implementing a new tire designation for them (other than M&S).

Numerous winter tires are available from various tire manufacturers, such as

Firestone, Michelin, Pirelli, and others. An example of these winter tires is the Bridgstone

Blizzak (<http://www.bsfs_usa.com/tech/apps/blizzak.htm>). This tire was developed in

Japan following the banning of studded tires there. It was first introduced into the U.S.

market in 1993. The following describes how the tire works:

The Blizzak ice and snow tire features a patented tread rubber compoundwhich was developed to deliver ice and snow performance without the useof studs. The Blizzak was the first tire designed using a multicell treadcompound with millions of microscopic pores that help stick to ice byremoving the thin layer of surface water that can allow a car to slide. Inwinter, when a surface of ice or snow comes under pressure from a tire, afilm of water is created. It is this film of water that causes icy roads to beslippery. As this water deepens, the tire's grip decreases making slippagemore likely.

The Multicell compound contains millions of microscopic pores. It is thesepores which cut through and disperse water away from the tire and icy roadsurfaces. The result; the tread contact area is increased and greater grip isachieved. The microscopic pores on the tread surface not only help eliminatethe film of water, but also create the "edge effect." The result: each edge ofthe pores bites the road surface creating greater driving and braking forces.

Throughout the life of the Multicell compound, new microscopic pores arecontinuously exposed on the tread surface. This helps ensure waterdispersion and greater grip on ice throughout the life of the Multicellcompound.

Exclusive Tracpoint sipes provide thousands of edges to help bite throughsnow, as well as help improve traction on icy roads. Lateral edges provide

B-2

excellent grip when accelerating and braking, while lengthwise edges helpprevent sideways slippage.

Blizzaks on all wheels - Due to the revolutionary traction capabilities of theBlizzak, Bridgestone recommends using Blizzaks only in sets of four toprovide the best handling characteristics and tire performance.

—(from <http://www.tirerack.com/tires/bridgestone/bs_blizz.htm>)

This new family of winter tires certainly has both advantages (good snow and ice

performance, no studs) and disadvantages (cost, high tread wear rates, speed restrictions). It

is not unreasonable to speculate that these studless winter tires will eventually reduce

studded tire usage rages.

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